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href="#Weak_interaction"> <div class="vector-toc-text"> 3.3 Weak interaction </div> </a> <ul id="toc-Weak_interaction-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Mass" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Mass"> <div class="vector-toc-text"> 3.4 Mass </div> </a> <ul id="toc-Mass-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Lepton_flavor_quantum_numbers" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Lepton_flavor_quantum_numbers"> <div class="vector-toc-text"> 3.5 Lepton flavor quantum numbers </div> </a> <ul id="toc-Lepton_flavor_quantum_numbers-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Universality" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Universality"> <div class="vector-toc-text"> 4 Universality </div> </a> <ul id="toc-Universality-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Table_of_leptons" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Table_of_leptons"> <div class="vector-toc-text"> 5 Table of leptons </div> </a> <ul id="toc-Table_of_leptons-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> 6 See also </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Notes" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Notes"> <div class="vector-toc-text"> 7 Notes </div> </a> <ul id="toc-Notes-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> 8 References </div> </a> <button aria-controls="toc-References-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> Toggle References subsection </button> <ul id="toc-References-sublist" class="vector-toc-list"> <li id="toc-Bibliography" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Bibliography"> <div class="vector-toc-text"> 8.1 Bibliography </div> </a> <ul id="toc-Bibliography-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> 9 External links </div> </a> <ul id="toc-External_links-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" title="Table of Contents" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" > Toggle the table of contents </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading">Lepton</h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. Available in 80 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-80" aria-hidden="true" > 80 languages </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-af mw-list-item"><a href="https://af.wikipedia.org/wiki/Lepton" title="Lepton – Afrikaans" lang="af" hreflang="af" data-title="Lepton" data-language-autonym="Afrikaans" data-language-local-name="Afrikaans" class="interlanguage-link-target">Afrikaans</a></li><li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D9%84%D8%A8%D8%AA%D9%88%D9%86_(%D9%81%D9%8A%D8%B2%D9%8A%D8%A7%D8%A1)" title="لبتون (فيزياء) – Arabic" lang="ar" hreflang="ar" data-title="لبتون (فيزياء)" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target">العربية</a></li><li class="interlanguage-link interwiki-ast mw-list-item"><a href="https://ast.wikipedia.org/wiki/Lept%C3%B3n" title="Leptón – Asturian" lang="ast" hreflang="ast" data-title="Leptón" data-language-autonym="Asturianu" data-language-local-name="Asturian" class="interlanguage-link-target">Asturianu</a></li><li class="interlanguage-link interwiki-az mw-list-item"><a href="https://az.wikipedia.org/wiki/Lepton" title="Lepton – Azerbaijani" lang="az" hreflang="az" data-title="Lepton" data-language-autonym="Azərbaycanca" data-language-local-name="Azerbaijani" class="interlanguage-link-target">Azərbaycanca</a></li><li class="interlanguage-link interwiki-azb mw-list-item"><a href="https://azb.wikipedia.org/wiki/%D9%84%D9%BE%D8%AA%D9%88%D9%86" title="لپتون – South Azerbaijani" lang="azb" hreflang="azb" data-title="لپتون" data-language-autonym="تۆرکجه" data-language-local-name="South Azerbaijani" class="interlanguage-link-target">تۆرکجه</a></li><li class="interlanguage-link interwiki-be mw-list-item"><a href="https://be.wikipedia.org/wiki/%D0%9B%D0%B5%D0%BF%D1%82%D0%BE%D0%BD" title="Лептон – Belarusian" lang="be" hreflang="be" data-title="Лептон" data-language-autonym="Беларуская" data-language-local-name="Belarusian" class="interlanguage-link-target">Беларуская</a></li><li class="interlanguage-link interwiki-bg mw-list-item"><a href="https://bg.wikipedia.org/wiki/%D0%9B%D0%B5%D0%BF%D1%82%D0%BE%D0%BD" title="Лептон – Bulgarian" lang="bg" hreflang="bg" data-title="Лептон" data-language-autonym="Български" data-language-local-name="Bulgarian" class="interlanguage-link-target">Български</a></li><li class="interlanguage-link interwiki-bs mw-list-item"><a href="https://bs.wikipedia.org/wiki/Lepton" title="Lepton – Bosnian" lang="bs" hreflang="bs" data-title="Lepton" data-language-autonym="Bosanski" data-language-local-name="Bosnian" class="interlanguage-link-target">Bosanski</a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Lept%C3%B3" title="Leptó – Catalan" lang="ca" hreflang="ca" data-title="Leptó" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target">Català</a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/Lepton" title="Lepton – Czech" lang="cs" hreflang="cs" data-title="Lepton" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target">Čeština</a></li><li class="interlanguage-link interwiki-cy mw-list-item"><a href="https://cy.wikipedia.org/wiki/Lepton" title="Lepton – Welsh" lang="cy" hreflang="cy" data-title="Lepton" data-language-autonym="Cymraeg" data-language-local-name="Welsh" class="interlanguage-link-target">Cymraeg</a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/Lepton" title="Lepton – Danish" lang="da" hreflang="da" data-title="Lepton" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target">Dansk</a></li><li class="interlanguage-link interwiki-ary mw-list-item"><a href="https://ary.wikipedia.org/wiki/%D9%84%D9%8A%D9%BE%D8%B7%D9%88%D9%86" title="ليپطون – Moroccan Arabic" lang="ary" hreflang="ary" data-title="ليپطون" data-language-autonym="الدارجة" data-language-local-name="Moroccan Arabic" class="interlanguage-link-target">الدارجة</a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Lepton" title="Lepton – German" lang="de" hreflang="de" data-title="Lepton" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target">Deutsch</a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/Leptonid" title="Leptonid – Estonian" lang="et" hreflang="et" data-title="Leptonid" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target">Eesti</a></li><li class="interlanguage-link interwiki-el mw-list-item"><a href="https://el.wikipedia.org/wiki/%CE%9B%CE%B5%CF%80%CF%84%CF%8C%CE%BD%CE%B9%CE%BF" title="Λεπτόνιο – Greek" lang="el" hreflang="el" data-title="Λεπτόνιο" data-language-autonym="Ελληνικά" data-language-local-name="Greek" class="interlanguage-link-target">Ελληνικά</a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Lept%C3%B3n" title="Leptón – Spanish" lang="es" hreflang="es" data-title="Leptón" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target">Español</a></li><li class="interlanguage-link interwiki-eo mw-list-item"><a href="https://eo.wikipedia.org/wiki/Leptono" title="Leptono – Esperanto" lang="eo" hreflang="eo" data-title="Leptono" data-language-autonym="Esperanto" data-language-local-name="Esperanto" class="interlanguage-link-target">Esperanto</a></li><li class="interlanguage-link interwiki-eu mw-list-item"><a href="https://eu.wikipedia.org/wiki/Leptoi" title="Leptoi – Basque" lang="eu" hreflang="eu" data-title="Leptoi" data-language-autonym="Euskara" data-language-local-name="Basque" class="interlanguage-link-target">Euskara</a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D9%84%D9%BE%D8%AA%D9%88%D9%86" title="لپتون – Persian" lang="fa" hreflang="fa" data-title="لپتون" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target">فارسی</a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Lepton" title="Lepton – French" lang="fr" hreflang="fr" data-title="Lepton" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target">Français</a></li><li class="interlanguage-link interwiki-ga mw-list-item"><a href="https://ga.wikipedia.org/wiki/Leapt%C3%B3n" title="Leaptón – Irish" lang="ga" hreflang="ga" data-title="Leaptón" data-language-autonym="Gaeilge" data-language-local-name="Irish" class="interlanguage-link-target">Gaeilge</a></li><li class="interlanguage-link interwiki-gl mw-list-item"><a href="https://gl.wikipedia.org/wiki/Lept%C3%B3n" title="Leptón – Galician" lang="gl" hreflang="gl" data-title="Leptón" data-language-autonym="Galego" data-language-local-name="Galician" class="interlanguage-link-target">Galego</a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EB%A0%99%ED%86%A4" title="렙톤 – Korean" lang="ko" hreflang="ko" data-title="렙톤" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target">한국어</a></li><li class="interlanguage-link interwiki-hy mw-list-item"><a href="https://hy.wikipedia.org/wiki/%D4%BC%D5%A5%D5%BA%D5%BF%D5%B8%D5%B6" title="Լեպտոն – Armenian" lang="hy" hreflang="hy" data-title="Լեպտոն" data-language-autonym="Հայերեն" data-language-local-name="Armenian" class="interlanguage-link-target">Հայերեն</a></li><li class="interlanguage-link interwiki-hi mw-list-item"><a href="https://hi.wikipedia.org/wiki/%E0%A4%B2%E0%A5%87%E0%A4%AA%E0%A5%8D%E0%A4%9F%E0%A5%89%E0%A4%A8" title="लेप्टॉन – Hindi" lang="hi" hreflang="hi" data-title="लेप्टॉन" data-language-autonym="हिन्दी" data-language-local-name="Hindi" class="interlanguage-link-target">हिन्दी</a></li><li class="interlanguage-link interwiki-hr mw-list-item"><a href="https://hr.wikipedia.org/wiki/Lepton" title="Lepton – Croatian" lang="hr" hreflang="hr" data-title="Lepton" data-language-autonym="Hrvatski" data-language-local-name="Croatian" class="interlanguage-link-target">Hrvatski</a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Lepton" title="Lepton – Indonesian" lang="id" hreflang="id" data-title="Lepton" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target">Bahasa Indonesia</a></li><li class="interlanguage-link interwiki-ia mw-list-item"><a href="https://ia.wikipedia.org/wiki/Lepton" title="Lepton – Interlingua" lang="ia" hreflang="ia" data-title="Lepton" data-language-autonym="Interlingua" data-language-local-name="Interlingua" class="interlanguage-link-target">Interlingua</a></li><li class="interlanguage-link interwiki-is mw-list-item"><a href="https://is.wikipedia.org/wiki/L%C3%A9tteind" title="Létteind – Icelandic" lang="is" hreflang="is" data-title="Létteind" data-language-autonym="Íslenska" data-language-local-name="Icelandic" class="interlanguage-link-target">Íslenska</a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Leptone" title="Leptone – Italian" lang="it" hreflang="it" data-title="Leptone" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target">Italiano</a></li><li class="interlanguage-link interwiki-he mw-list-item"><a href="https://he.wikipedia.org/wiki/%D7%9C%D7%A4%D7%98%D7%95%D7%9F" title="לפטון – Hebrew" lang="he" hreflang="he" data-title="לפטון" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target">עברית</a></li><li class="interlanguage-link interwiki-kn mw-list-item"><a href="https://kn.wikipedia.org/wiki/%E0%B2%B2%E0%B3%86%E0%B2%AA%E0%B3%8D%E0%B2%9F%E0%B2%BE%E0%B2%A8%E0%B3%8D" title="ಲೆಪ್ಟಾನ್ – Kannada" lang="kn" hreflang="kn" data-title="ಲೆಪ್ಟಾನ್" data-language-autonym="ಕನ್ನಡ" data-language-local-name="Kannada" class="interlanguage-link-target">ಕನ್ನಡ</a></li><li class="interlanguage-link interwiki-ka mw-list-item"><a href="https://ka.wikipedia.org/wiki/%E1%83%9A%E1%83%94%E1%83%9E%E1%83%A2%E1%83%9D%E1%83%9C%E1%83%98" title="ლეპტონი – Georgian" lang="ka" hreflang="ka" data-title="ლეპტონი" data-language-autonym="ქართული" data-language-local-name="Georgian" class="interlanguage-link-target">ქართული</a></li><li class="interlanguage-link interwiki-kk mw-list-item"><a href="https://kk.wikipedia.org/wiki/%D0%9B%D0%B5%D0%BF%D1%82%D0%BE%D0%BD" title="Лептон – Kazakh" lang="kk" hreflang="kk" data-title="Лептон" data-language-autonym="Қазақша" data-language-local-name="Kazakh" class="interlanguage-link-target">Қазақша</a></li><li class="interlanguage-link interwiki-ky mw-list-item"><a href="https://ky.wikipedia.org/wiki/%D0%9B%D0%B5%D0%BF%D1%82%D0%BE%D0%BD%D0%B4%D0%BE%D1%80" title="Лептондор – Kyrgyz" lang="ky" hreflang="ky" data-title="Лептондор" data-language-autonym="Кыргызча" data-language-local-name="Kyrgyz" class="interlanguage-link-target">Кыргызча</a></li><li class="interlanguage-link interwiki-la mw-list-item"><a href="https://la.wikipedia.org/wiki/Lepton" title="Lepton – Latin" lang="la" hreflang="la" data-title="Lepton" data-language-autonym="Latina" data-language-local-name="Latin" class="interlanguage-link-target">Latina</a></li><li class="interlanguage-link interwiki-lv mw-list-item"><a href="https://lv.wikipedia.org/wiki/Leptoni" title="Leptoni – Latvian" lang="lv" hreflang="lv" data-title="Leptoni" data-language-autonym="Latviešu" data-language-local-name="Latvian" class="interlanguage-link-target">Latviešu</a></li><li class="interlanguage-link interwiki-lb mw-list-item"><a href="https://lb.wikipedia.org/wiki/Lepton" title="Lepton – Luxembourgish" lang="lb" hreflang="lb" data-title="Lepton" data-language-autonym="Lëtzebuergesch" data-language-local-name="Luxembourgish" class="interlanguage-link-target">Lëtzebuergesch</a></li><li class="interlanguage-link interwiki-lt mw-list-item"><a href="https://lt.wikipedia.org/wiki/Leptonas" title="Leptonas – Lithuanian" lang="lt" hreflang="lt" data-title="Leptonas" data-language-autonym="Lietuvių" data-language-local-name="Lithuanian" class="interlanguage-link-target">Lietuvių</a></li><li class="interlanguage-link interwiki-li mw-list-item"><a href="https://li.wikipedia.org/wiki/Lepton" title="Lepton – Limburgish" lang="li" hreflang="li" data-title="Lepton" data-language-autonym="Limburgs" data-language-local-name="Limburgish" class="interlanguage-link-target">Limburgs</a></li><li class="interlanguage-link interwiki-hu mw-list-item"><a href="https://hu.wikipedia.org/wiki/Lepton" title="Lepton – Hungarian" lang="hu" hreflang="hu" data-title="Lepton" data-language-autonym="Magyar" data-language-local-name="Hungarian" class="interlanguage-link-target">Magyar</a></li><li class="interlanguage-link interwiki-ml mw-list-item"><a href="https://ml.wikipedia.org/wiki/%E0%B4%B2%E0%B5%86%E0%B4%AA%E0%B5%8D%E0%B4%B1%E0%B5%8D%E0%B4%B1%E0%B5%BA" title="ലെപ്റ്റൺ – Malayalam" lang="ml" hreflang="ml" data-title="ലെപ്റ്റൺ" data-language-autonym="മലയാളം" data-language-local-name="Malayalam" class="interlanguage-link-target">മലയാളം</a></li><li class="interlanguage-link interwiki-ms mw-list-item"><a href="https://ms.wikipedia.org/wiki/Lepton" title="Lepton – Malay" lang="ms" hreflang="ms" data-title="Lepton" data-language-autonym="Bahasa Melayu" data-language-local-name="Malay" class="interlanguage-link-target">Bahasa Melayu</a></li><li class="interlanguage-link interwiki-mn mw-list-item"><a href="https://mn.wikipedia.org/wiki/%D0%9B%D0%B5%D0%BF%D1%82%D0%BE%D0%BD" title="Лептон – Mongolian" lang="mn" hreflang="mn" data-title="Лептон" data-language-autonym="Монгол" data-language-local-name="Mongolian" class="interlanguage-link-target">Монгол</a></li><li class="interlanguage-link interwiki-my mw-list-item"><a href="https://my.wikipedia.org/wiki/%E1%80%9C%E1%80%80%E1%80%BA%E1%80%95%E1%80%90%E1%80%BD%E1%80%94%E1%80%BA" title="လက်ပတွန် – Burmese" lang="my" hreflang="my" data-title="လက်ပတွန်" data-language-autonym="မြန်မာဘာသာ" data-language-local-name="Burmese" class="interlanguage-link-target">မြန်မာဘာသာ</a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Lepton_(subatomair_deeltje)" title="Lepton (subatomair deeltje) – Dutch" lang="nl" hreflang="nl" data-title="Lepton (subatomair deeltje)" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target">Nederlands</a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E3%83%AC%E3%83%97%E3%83%88%E3%83%B3_(%E7%B4%A0%E7%B2%92%E5%AD%90)" title="レプトン (素粒子) – Japanese" lang="ja" hreflang="ja" data-title="レプトン (素粒子)" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target">日本語</a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Lepton" title="Lepton – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Lepton" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target">Norsk bokmål</a></li><li class="interlanguage-link interwiki-nn mw-list-item"><a href="https://nn.wikipedia.org/wiki/Lepton" title="Lepton – Norwegian Nynorsk" lang="nn" hreflang="nn" data-title="Lepton" data-language-autonym="Norsk nynorsk" data-language-local-name="Norwegian Nynorsk" class="interlanguage-link-target">Norsk nynorsk</a></li><li class="interlanguage-link interwiki-oc mw-list-item"><a href="https://oc.wikipedia.org/wiki/Lepton" title="Lepton – Occitan" lang="oc" hreflang="oc" data-title="Lepton" data-language-autonym="Occitan" data-language-local-name="Occitan" class="interlanguage-link-target">Occitan</a></li><li class="interlanguage-link interwiki-uz mw-list-item"><a href="https://uz.wikipedia.org/wiki/Lepton" title="Lepton – Uzbek" lang="uz" hreflang="uz" data-title="Lepton" data-language-autonym="Oʻzbekcha / ўзбекча" data-language-local-name="Uzbek" class="interlanguage-link-target">Oʻzbekcha / ўзбекча</a></li><li class="interlanguage-link interwiki-pa mw-list-item"><a href="https://pa.wikipedia.org/wiki/%E0%A8%B2%E0%A9%88%E0%A8%AA%E0%A8%9F%E0%A9%8C%E0%A8%A8" title="ਲੈਪਟੌਨ – Punjabi" lang="pa" hreflang="pa" data-title="ਲੈਪਟੌਨ" data-language-autonym="ਪੰਜਾਬੀ" data-language-local-name="Punjabi" class="interlanguage-link-target">ਪੰਜਾਬੀ</a></li><li class="interlanguage-link interwiki-pnb mw-list-item"><a href="https://pnb.wikipedia.org/wiki/%D9%84%DB%8C%D9%BE%D9%B9%D9%88%D9%86" title="لیپٹون – Western Punjabi" lang="pnb" hreflang="pnb" data-title="لیپٹون" data-language-autonym="پنجابی" data-language-local-name="Western Punjabi" class="interlanguage-link-target">پنجابی</a></li><li class="interlanguage-link interwiki-nds mw-list-item"><a href="https://nds.wikipedia.org/wiki/Lepton" title="Lepton – Low German" lang="nds" hreflang="nds" data-title="Lepton" data-language-autonym="Plattdüütsch" data-language-local-name="Low German" class="interlanguage-link-target">Plattdüütsch</a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Lepton_(mechanika_kwantowa)" title="Lepton (mechanika kwantowa) – Polish" lang="pl" hreflang="pl" data-title="Lepton (mechanika kwantowa)" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target">Polski</a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/L%C3%A9pton" title="Lépton – Portuguese" lang="pt" hreflang="pt" data-title="Lépton" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target">Português</a></li><li class="interlanguage-link interwiki-kaa mw-list-item"><a href="https://kaa.wikipedia.org/wiki/Lepton" title="Lepton – Kara-Kalpak" lang="kaa" hreflang="kaa" data-title="Lepton" data-language-autonym="Qaraqalpaqsha" data-language-local-name="Kara-Kalpak" class="interlanguage-link-target">Qaraqalpaqsha</a></li><li class="interlanguage-link interwiki-ro mw-list-item"><a href="https://ro.wikipedia.org/wiki/Lepton" title="Lepton – Romanian" lang="ro" hreflang="ro" data-title="Lepton" data-language-autonym="Română" data-language-local-name="Romanian" class="interlanguage-link-target">Română</a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%9B%D0%B5%D0%BF%D1%82%D0%BE%D0%BD%D1%8B" title="Лептоны – Russian" lang="ru" hreflang="ru" data-title="Лептоны" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target">Русский</a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Lepton" title="Lepton – Simple English" lang="en-simple" hreflang="en-simple" data-title="Lepton" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target">Simple English</a></li><li class="interlanguage-link interwiki-sk mw-list-item"><a href="https://sk.wikipedia.org/wiki/Lept%C3%B3n" title="Leptón – Slovak" lang="sk" hreflang="sk" data-title="Leptón" data-language-autonym="Slovenčina" data-language-local-name="Slovak" class="interlanguage-link-target">Slovenčina</a></li><li class="interlanguage-link interwiki-sl mw-list-item"><a href="https://sl.wikipedia.org/wiki/Lepton" title="Lepton – Slovenian" lang="sl" hreflang="sl" data-title="Lepton" data-language-autonym="Slovenščina" data-language-local-name="Slovenian" class="interlanguage-link-target">Slovenščina</a></li><li class="interlanguage-link interwiki-sr mw-list-item"><a href="https://sr.wikipedia.org/wiki/%D0%9B%D0%B5%D0%BF%D1%82%D0%BE%D0%BD" title="Лептон – Serbian" lang="sr" hreflang="sr" data-title="Лептон" data-language-autonym="Српски / srpski" data-language-local-name="Serbian" class="interlanguage-link-target">Српски / srpski</a></li><li class="interlanguage-link interwiki-sh mw-list-item"><a href="https://sh.wikipedia.org/wiki/Lepton" title="Lepton – Serbo-Croatian" lang="sh" hreflang="sh" data-title="Lepton" data-language-autonym="Srpskohrvatski / српскохрватски" data-language-local-name="Serbo-Croatian" class="interlanguage-link-target">Srpskohrvatski / српскохрватски</a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/Leptoni" title="Leptoni – Finnish" lang="fi" hreflang="fi" data-title="Leptoni" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target">Suomi</a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/Lepton" title="Lepton – Swedish" lang="sv" hreflang="sv" data-title="Lepton" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target">Svenska</a></li><li class="interlanguage-link interwiki-tl mw-list-item"><a href="https://tl.wikipedia.org/wiki/Lepton" title="Lepton – Tagalog" lang="tl" hreflang="tl" data-title="Lepton" data-language-autonym="Tagalog" data-language-local-name="Tagalog" class="interlanguage-link-target">Tagalog</a></li><li class="interlanguage-link interwiki-ta mw-list-item"><a href="https://ta.wikipedia.org/wiki/%E0%AE%AE%E0%AF%86%E0%AE%A9%E0%AF%8D%E0%AE%AE%E0%AE%BF" title="மென்மி – Tamil" lang="ta" hreflang="ta" data-title="மென்மி" data-language-autonym="தமிழ்" data-language-local-name="Tamil" class="interlanguage-link-target">தமிழ்</a></li><li class="interlanguage-link interwiki-tt mw-list-item"><a href="https://tt.wikipedia.org/wiki/%D0%9B%D0%B5%D0%BF%D1%82%D0%BE%D0%BD" title="Лептон – Tatar" lang="tt" hreflang="tt" data-title="Лептон" data-language-autonym="Татарча / tatarça" data-language-local-name="Tatar" class="interlanguage-link-target">Татарча / tatarça</a></li><li class="interlanguage-link interwiki-th mw-list-item"><a href="https://th.wikipedia.org/wiki/%E0%B9%80%E0%B8%A5%E0%B8%9B%E0%B8%95%E0%B8%AD%E0%B8%99" title="เลปตอน – Thai" lang="th" hreflang="th" data-title="เลปตอน" data-language-autonym="ไทย" data-language-local-name="Thai" class="interlanguage-link-target">ไทย</a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/Lepton" title="Lepton – Turkish" lang="tr" hreflang="tr" data-title="Lepton" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target">Türkçe</a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%9B%D0%B5%D0%BF%D1%82%D0%BE%D0%BD" title="Лептон – Ukrainian" lang="uk" hreflang="uk" data-title="Лептон" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target">Українська</a></li><li class="interlanguage-link interwiki-ur mw-list-item"><a href="https://ur.wikipedia.org/wiki/%D9%86%D8%AD%DB%8C%D9%81%DB%81" title="نحیفہ – Urdu" lang="ur" hreflang="ur" data-title="نحیفہ" data-language-autonym="اردو" data-language-local-name="Urdu" class="interlanguage-link-target">اردو</a></li><li class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/Lepton" title="Lepton – Vietnamese" lang="vi" hreflang="vi" data-title="Lepton" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target">Tiếng Việt</a></li><li class="interlanguage-link interwiki-war mw-list-item"><a href="https://war.wikipedia.org/wiki/Lepton" title="Lepton – Waray" lang="war" hreflang="war" data-title="Lepton" data-language-autonym="Winaray" data-language-local-name="Waray" class="interlanguage-link-target">Winaray</a></li><li class="interlanguage-link interwiki-wo mw-list-item"><a href="https://wo.wikipedia.org/wiki/Lepton" title="Lepton – Wolof" lang="wo" hreflang="wo" data-title="Lepton" data-language-autonym="Wolof" data-language-local-name="Wolof" class="interlanguage-link-target">Wolof</a></li><li class="interlanguage-link interwiki-wuu mw-list-item"><a href="https://wuu.wikipedia.org/wiki/%E8%BD%BB%E5%AD%90" title="轻子 – Wu" lang="wuu" hreflang="wuu" data-title="轻子" data-language-autonym="吴语" data-language-local-name="Wu" class="interlanguage-link-target">吴语</a></li><li class="interlanguage-link interwiki-zh-yue mw-list-item"><a href="https://zh-yue.wikipedia.org/wiki/%E8%BC%95%E5%AD%90" title="輕子 – Cantonese" lang="yue" hreflang="yue" data-title="輕子" data-language-autonym="粵語" data-language-local-name="Cantonese" class="interlanguage-link-target">粵語</a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E8%BC%95%E5%AD%90" title="輕子 – Chinese" lang="zh" hreflang="zh" data-title="輕子" data-language-autonym="中文" data-language-local-name="Chinese" class="interlanguage-link-target">中文</a></li> </ul> 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data-mw-ve-target-container> <div class="vector-body-before-content"> <div class="mw-indicators"> </div> <div id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Class of elementary particles</div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">Not to be confused with <a href="/wiki/Leptin" title="Leptin">leptin</a> or <a href="/wiki/Lipton" title="Lipton">Lipton</a>.</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">For other uses, see <a href="/wiki/Lepton_(disambiguation)" class="mw-disambig" title="Lepton (disambiguation)">Lepton (disambiguation)</a>.</div> <table class="wikitable" style="text-align:center; float:right; margin:0em 0em 0em 1em;"> <caption>Generations of matter </caption> <tbody><tr> <th colspan="2"><a href="/wiki/Fermion" title="Fermion">Fermion</a> categories </th> <th colspan="3"><a href="/wiki/Elementary_particle" title="Elementary particle">Elementary particle</a> <a href="/wiki/Generation_(particle_physics)" title="Generation (particle physics)">generation</a> </th></tr> <tr> <th> Type </th> <th> Subtype </th> <th> First </th> <th> Second </th> <th> Third </th></tr> <tr> <th rowspan="2"><a href="/wiki/Quark" title="Quark">Quarks</a> (<a href="/wiki/Color_(quantum_mechanics)" class="mw-redirect" title="Color (quantum mechanics)">colored</a>) </th> <th>down-type </th> <td><a href="/wiki/Down_quark" title="Down quark">down</a> </td> <td><a href="/wiki/Strange_quark" title="Strange quark">strange</a> </td> <td><a href="/wiki/Bottom_quark" title="Bottom quark">bottom</a> </td></tr> <tr> <th>up-type </th> <td><a href="/wiki/Up_quark" title="Up quark">up</a> </td> <td><a href="/wiki/Charm_quark" title="Charm quark">charm</a> </td> <td><a href="/wiki/Top_quark" title="Top quark">top</a> </td></tr> <tr> <th rowspan="2"><a class="mw-selflink selflink">Leptons</a> (color-free) </th> <th>charged </th> <td><a href="/wiki/Electron" title="Electron">electron</a> </td> <td><a href="/wiki/Muon" title="Muon">muon</a> </td> <td><a href="/wiki/Tau_(particle)" title="Tau (particle)">tau</a> </td></tr> <tr> <th> <a href="/wiki/Neutrino" title="Neutrino">neutral</a> </th> <td> <a href="/wiki/Electron_neutrino" title="Electron neutrino">electron neutrino</a> </td> <td> <a href="/wiki/Muon_neutrino" title="Muon neutrino">muon neutrino</a> </td> <td> <a href="/wiki/Tau_neutrino" title="Tau neutrino">tau neutrino</a> </td></tr></tbody></table> <style data-mw-deduplicate="TemplateStyles:r1257001546">.mw-parser-output .infobox-subbox{padding:0;border:none;margin:-3px;width:auto;min-width:100%;font-size:100%;clear:none;float:none;background-color:transparent}.mw-parser-output .infobox-3cols-child{margin:auto}.mw-parser-output .infobox .navbar{font-size:100%}@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-full-data:not(.notheme)>div:not(.notheme)[style]{background:#1f1f23!important;color:#f8f9fa}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-full-data:not(.notheme) div:not(.notheme){background:#1f1f23!important;color:#f8f9fa}}@media(min-width:640px){body.skin--responsive .mw-parser-output .infobox-table{display:table!important}body.skin--responsive .mw-parser-output .infobox-table>caption{display:table-caption!important}body.skin--responsive .mw-parser-output .infobox-table>tbody{display:table-row-group}body.skin--responsive .mw-parser-output .infobox-table tr{display:table-row!important}body.skin--responsive .mw-parser-output .infobox-table th,body.skin--responsive .mw-parser-output .infobox-table td{padding-left:inherit;padding-right:inherit}}</style><table class="infobox"><caption class="infobox-title">Lepton</caption><tbody><tr><td colspan="2" class="infobox-image"><a href="/wiki/File:Beta_Negative_Decay.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/8/89/Beta_Negative_Decay.svg/200px-Beta_Negative_Decay.svg.png" decoding="async" width="200" height="200" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/89/Beta_Negative_Decay.svg/300px-Beta_Negative_Decay.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/89/Beta_Negative_Decay.svg/400px-Beta_Negative_Decay.svg.png 2x" data-file-width="400" data-file-height="400" /></a><div class="infobox-caption">Leptons are involved in several processes such as <a href="/wiki/Beta_decay" title="Beta decay">beta decay</a>.</div></td></tr><tr><th scope="row" class="infobox-label"><a href="/wiki/Particle#Composition" title="Particle">Composition</a></th><td class="infobox-data"><a href="/wiki/Elementary_particle" title="Elementary particle">Elementary particle</a></td></tr><tr><th scope="row" class="infobox-label"><a href="/wiki/Particle_statistics" title="Particle statistics">Statistics</a></th><td class="infobox-data"><a href="/wiki/Fermionic" class="mw-redirect" title="Fermionic">Fermionic</a></td></tr><tr><th scope="row" class="infobox-label"><a href="/wiki/Generation_(particle_physics)" title="Generation (particle physics)">Generation</a></th><td class="infobox-data">1st, 2nd, 3rd</td></tr><tr><th scope="row" class="infobox-label"><a href="/wiki/Fundamental_interaction" title="Fundamental interaction">Interactions</a></th><td class="infobox-data"><a href="/wiki/Electromagnetism" title="Electromagnetism">Electromagnetism</a>, <a href="/wiki/Gravitation" class="mw-redirect" title="Gravitation">gravitation</a>, <a href="/wiki/Weak_interaction" title="Weak interaction">weak</a></td></tr><tr><th scope="row" class="infobox-label">Symbol</th><td class="infobox-data"> ℓ </td></tr><tr><th scope="row" class="infobox-label"><a href="/wiki/Antiparticle" title="Antiparticle">Antiparticle</a></th><td class="infobox-data">Antilepton ( ℓ )</td></tr><tr><th scope="row" class="infobox-label">Types</th><td class="infobox-data">6 (<a href="/wiki/Electron" title="Electron">electron</a>, <a href="/wiki/Electron_neutrino" title="Electron neutrino">electron neutrino</a>, <a href="/wiki/Muon" title="Muon">muon</a>, <a href="/wiki/Muon_neutrino" title="Muon neutrino">muon neutrino</a>, <a href="/wiki/Tau_(particle)" title="Tau (particle)">tau</a>, <a href="/wiki/Tau_neutrino" title="Tau neutrino">tau neutrino</a>)</td></tr><tr><th scope="row" class="infobox-label"><a href="/wiki/Electric_charge" title="Electric charge">Electric charge</a></th><td class="infobox-data">+1 <a href="/wiki/Elementary_charge" title="Elementary charge">e</a>, 0 e, −1 e</td></tr><tr><th scope="row" class="infobox-label"><a href="/wiki/Color_charge" title="Color charge">Color charge</a></th><td class="infobox-data">No</td></tr><tr><th scope="row" class="infobox-label"><a href="/wiki/Spin_(physics)" title="Spin (physics)">Spin</a></th><td class="infobox-data"><style data-mw-deduplicate="TemplateStyles:r1214402035">.mw-parser-output .sfrac{white-space:nowrap}.mw-parser-output .sfrac.tion,.mw-parser-output .sfrac .tion{display:inline-block;vertical-align:-0.5em;font-size:85%;text-align:center}.mw-parser-output .sfrac .num{display:block;line-height:1em;margin:0.0em 0.1em;border-bottom:1px solid}.mw-parser-output .sfrac .den{display:block;line-height:1em;margin:0.1em 0.1em}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}</style>⁠1/2⁠ <a href="/wiki/Reduced_Planck_constant" class="mw-redirect" title="Reduced Planck constant">ħ</a></td></tr><tr><th scope="row" class="infobox-label"><a href="/wiki/Baryon_number" title="Baryon number">Baryon number</a></th><td class="infobox-data">0</td></tr></tbody></table> <style data-mw-deduplicate="TemplateStyles:r1235681985">.mw-parser-output .side-box{margin:4px 0;box-sizing:border-box;border:1px solid #aaa;font-size:88%;line-height:1.25em;background-color:var(--background-color-interactive-subtle,#f8f9fa);display:flow-root}.mw-parser-output .side-box-abovebelow,.mw-parser-output .side-box-text{padding:0.25em 0.9em}.mw-parser-output .side-box-image{padding:2px 0 2px 0.9em;text-align:center}.mw-parser-output .side-box-imageright{padding:2px 0.9em 2px 0;text-align:center}@media(min-width:500px){.mw-parser-output .side-box-flex{display:flex;align-items:center}.mw-parser-output .side-box-text{flex:1;min-width:0}}@media(min-width:720px){.mw-parser-output .side-box{width:238px}.mw-parser-output .side-box-right{clear:right;float:right;margin-left:1em}.mw-parser-output .side-box-left{margin-right:1em}}</style><style data-mw-deduplicate="TemplateStyles:r1092331828">@media(min-width:720px){.mw-parser-output .contains-special-characters{width:22em}}</style><div class="side-box metadata side-box-right contains-special-characters noprint selfref"><style data-mw-deduplicate="TemplateStyles:r1126788409">.mw-parser-output .plainlist ol,.mw-parser-output .plainlist ul{line-height:inherit;list-style:none;margin:0;padding:0}.mw-parser-output .plainlist ol li,.mw-parser-output .plainlist ul li{margin-bottom:0}</style> <div class="side-box-flex"> <div class="side-box-text plainlist">This article contains <a href="/wiki/Help:Special_characters" title="Help:Special characters">special characters</a>. Without proper <a href="/wiki/Help:Special_characters" title="Help:Special characters">rendering support</a>, you may see <a href="/wiki/Specials_(Unicode_block)#Replacement_character" title="Specials (Unicode block)">question marks, boxes, or other symbols</a>.</div></div> </div> In <a href="/wiki/Particle_physics" title="Particle physics">particle physics</a>, a lepton is an <a href="/wiki/Elementary_particle" title="Elementary particle">elementary particle</a> of <a href="/wiki/Half-integer_spin" class="mw-redirect" title="Half-integer spin">half-integer spin</a> (<a href="/wiki/Spin_(physics)" title="Spin (physics)">spin</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035" />⁠1/2⁠) that does not undergo <a href="/wiki/Strong_interaction" title="Strong interaction">strong interactions</a>.<a href="#cite_note-1">[1]</a> Two main classes of leptons exist: <a href="/wiki/Electric_charge" title="Electric charge">charged</a> leptons (also known as the <a href="/wiki/Electron" title="Electron">electron</a>-like leptons or muons), including the <a href="/wiki/Electron" title="Electron">electron</a>, <a href="/wiki/Muon" title="Muon">muon</a>, and <a href="/wiki/Tauon" class="mw-redirect" title="Tauon">tauon</a>, and neutral leptons, better known as <a href="/wiki/Neutrino" title="Neutrino">neutrinos</a>. Charged leptons can combine with other particles to form various <a href="/wiki/Composite_particle" class="mw-redirect" title="Composite particle">composite particles</a> such as <a href="/wiki/Atom" title="Atom">atoms</a> and <a href="/wiki/Positronium" title="Positronium">positronium</a>, while neutrinos rarely interact with anything, and are consequently rarely observed. The best known of all leptons is the <a href="/wiki/Electron" title="Electron">electron</a>. There are six types of leptons, known as <a href="/wiki/Flavour_(particle_physics)" title="Flavour (particle physics)">flavours</a>, grouped in three <a href="/wiki/Generation_(particle_physics)" title="Generation (particle physics)">generations</a>.<a href="#cite_note-HyperphysicsLepton-2">[2]</a> The <a href="/wiki/Standard_Model" title="Standard Model">first-generation</a> leptons, also called electronic leptons, comprise the <a href="/wiki/Electron" title="Electron">electron</a> ( e− ) and the <a href="/wiki/Electron_neutrino" title="Electron neutrino">electron neutrino</a> ( ν e); the second are the muonic leptons, comprising the <a href="/wiki/Muon" title="Muon">muon</a> ( μ− ) and the <a href="/wiki/Muon_neutrino" title="Muon neutrino">muon neutrino</a> ( ν μ); and the third are the tauonic leptons, comprising the <a href="/wiki/Tau_(particle)" title="Tau (particle)">tau</a> ( τ− ) and the <a href="/wiki/Tau_neutrino" title="Tau neutrino">tau neutrino</a> ( ν τ). Electrons have the least mass of all the charged leptons. The heavier muons and taus will rapidly change into electrons and neutrinos through a process of <a href="/wiki/Particle_decay" title="Particle decay">particle decay</a>: the transformation from a higher mass state to a lower mass state. Thus electrons are stable and the most common charged lepton in the <a href="/wiki/Universe" title="Universe">universe</a>, whereas muons and taus can only be produced in <a href="/wiki/High_energy_physics" class="mw-redirect" title="High energy physics">high-energy</a> collisions (such as those involving <a href="/wiki/Cosmic_ray" title="Cosmic ray">cosmic rays</a> and those carried out in <a href="/wiki/Particle_accelerator" title="Particle accelerator">particle accelerators</a>). Leptons have various <a href="/wiki/Intrinsic_properties" class="mw-redirect" title="Intrinsic properties">intrinsic properties</a>, including <a href="/wiki/Electric_charge" title="Electric charge">electric charge</a>, <a href="/wiki/Spin_(physics)" title="Spin (physics)">spin</a>, and <a href="/wiki/Mass" title="Mass">mass</a>. Unlike <a href="/wiki/Quark" title="Quark">quarks</a>, however, leptons are not subject to the <a href="/wiki/Strong_interaction" title="Strong interaction">strong interaction</a>, but they are subject to the other three <a href="/wiki/Fundamental_interaction" title="Fundamental interaction">fundamental interactions</a>: <a href="/wiki/Gravitation" class="mw-redirect" title="Gravitation">gravitation</a>, the <a href="/wiki/Weak_interaction" title="Weak interaction">weak interaction</a>, and to <a href="/wiki/Electromagnetism" title="Electromagnetism">electromagnetism</a>, of which the latter is proportional to charge, and is thus zero for the electrically neutral neutrinos. For every lepton flavor, there is a corresponding type of <a href="/wiki/Antiparticle" title="Antiparticle">antiparticle</a>, known as an antilepton, that differs from the lepton only in that some of its properties have <a href="/wiki/Charge_conjugation" class="mw-redirect" title="Charge conjugation">equal magnitude but opposite sign</a>. According to certain theories, neutrinos may be <a href="/wiki/Majorana_fermion" title="Majorana fermion">their own antiparticle</a>. It is not currently known whether this is the case. The first charged lepton, the electron, was theorized in the mid-19th century by several scientists<a href="#cite_note-farrar-3">[3]</a><a href="#cite_note-arabatzis-4">[4]</a><a href="#cite_note-buchwald1-5">[5]</a> and was discovered in 1897 by <a href="/wiki/J._J._Thomson" title="J. J. Thomson">J. J. Thomson</a>.<a href="#cite_note-thomson-6">[6]</a> The next lepton to be observed was the <a href="/wiki/Muon" title="Muon">muon</a>, discovered by <a href="/wiki/Carl_D._Anderson" class="mw-redirect" title="Carl D. Anderson">Carl D. Anderson</a> in 1936, which was classified as a <a href="/wiki/Meson" title="Meson">meson</a> at the time.<a href="#cite_note-7">[7]</a> After investigation, it was realized that the muon did not have the expected properties of a meson, but rather behaved like an electron, only with higher mass. It took until 1947 for the concept of "leptons" as a family of particles to be proposed.<a href="#cite_note-LAS-8">[8]</a> The first neutrino, the electron neutrino, was proposed by <a href="/wiki/Wolfgang_Pauli" title="Wolfgang Pauli">Wolfgang Pauli</a> in 1930 to explain certain characteristics of <a href="/wiki/Beta_decay" title="Beta decay">beta decay</a>.<a href="#cite_note-LAS-8">[8]</a> It was first observed in the <a href="/wiki/Cowan%E2%80%93Reines_neutrino_experiment" title="Cowan–Reines neutrino experiment">Cowan–Reines neutrino experiment</a> conducted by <a href="/wiki/Clyde_Cowan" title="Clyde Cowan">Clyde Cowan</a> and <a href="/wiki/Frederick_Reines" title="Frederick Reines">Frederick Reines</a> in 1956.<a href="#cite_note-LAS-8">[8]</a><a href="#cite_note-9">[9]</a> The muon neutrino was discovered in 1962 by <a href="/wiki/Leon_M._Lederman" title="Leon M. Lederman">Leon M. Lederman</a>, <a href="/wiki/Melvin_Schwartz" title="Melvin Schwartz">Melvin Schwartz</a>, and <a href="/wiki/Jack_Steinberger" title="Jack Steinberger">Jack Steinberger</a>,<a href="#cite_note-slac.stanford.edu-10">[10]</a> and the tau discovered between 1974 and 1977 by <a href="/wiki/Martin_Lewis_Perl" title="Martin Lewis Perl">Martin Lewis Perl</a> and his colleagues from the <a href="/wiki/Stanford_Linear_Accelerator_Center" class="mw-redirect" title="Stanford Linear Accelerator Center">Stanford Linear Accelerator Center</a> and <a href="/wiki/Lawrence_Berkeley_National_Laboratory" title="Lawrence Berkeley National Laboratory">Lawrence Berkeley National Laboratory</a>.<a href="#cite_note-11">[11]</a> The <a href="/wiki/Tau_neutrino" title="Tau neutrino">tau neutrino</a> remained elusive until July 2000, when the <a href="/wiki/DONUT" title="DONUT">DONUT</a> collaboration from <a href="/wiki/Fermilab" title="Fermilab">Fermilab</a> announced its discovery.<a href="#cite_note-tauonpress-12">[12]</a><a href="#cite_note-tauonpaper-13">[13]</a> Leptons are an important part of the <a href="/wiki/Standard_Model" title="Standard Model">Standard Model</a>. Electrons are one of the components of <a href="/wiki/Atom" title="Atom">atoms</a>, alongside <a href="/wiki/Proton" title="Proton">protons</a> and <a href="/wiki/Neutron" title="Neutron">neutrons</a>. <a href="/wiki/Exotic_atom" title="Exotic atom">Exotic atoms</a> with muons and taus instead of electrons can also be synthesized, as well as lepton–antilepton particles such as <a href="/wiki/Positronium" title="Positronium">positronium</a>. <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Etymology">Etymology</h2>[<a href="/w/index.php?title=Lepton&action=edit&section=1" title="Edit section: Etymology">edit</a>]</div> The name lepton comes from the <a href="/wiki/Ancient_Greek" title="Ancient Greek">Greek</a> λεπτός leptós, "fine, small, thin" (<a href="/wiki/Grammatical_gender" title="Grammatical gender">neuter</a> nominative/accusative singular form: λεπτόν leptón);<a href="#cite_note-14">[14]</a><a href="#cite_note-15">[15]</a> the earliest attested form of the word is the <a href="/wiki/Mycenaean_Greek" title="Mycenaean Greek">Mycenaean Greek</a> 𐀩𐀡𐀵, re-po-to, written in <a href="/wiki/Linear_B" title="Linear B">Linear B</a> syllabic script.<a href="#cite_note-16">[16]</a> Lepton was first used by physicist <a href="/wiki/L%C3%A9on_Rosenfeld" title="Léon Rosenfeld">Léon Rosenfeld</a> in 1948:<a href="#cite_note-17">[17]</a> <blockquote>Following a suggestion of Prof. <a href="/wiki/C._M%C3%B8ller" class="mw-redirect" title="C. Møller">C. Møller</a>, I adopt—as a pendant to "nucleon"—the denomination "lepton" (from λεπτός, small, thin, delicate) to denote a particle of small mass.</blockquote> Rosenfeld chose the name as the common name for electrons and (then hypothesized) neutrinos. Additionally, the muon, initially classified as a meson, was reclassified as a lepton in the 1950s. The masses of those particles are small compared to nucleons—the mass of an electron (0.511 <a href="/wiki/Electronvolt#Mass" title="Electronvolt">MeV/c2</a>)<a href="#cite_note-Electron-18">[18]</a> and the mass of a muon (with a value of 105.7 MeV/c2)<a href="#cite_note-Muon-19">[19]</a> are fractions of the mass of the "heavy" proton (938.3 MeV/c2), and the mass of a neutrino is nearly zero.<a href="#cite_note-Proton-20">[20]</a> However, the mass of the tau (discovered in the mid-1970s) (1777 MeV/c2)<a href="#cite_note-Tauon-21">[21]</a> is nearly twice that of the proton and 3477‍<a href="#cite_note-physconst-mtauome-22">[22]</a> times that of the electron. <div class="mw-heading mw-heading2"><h2 id="History">History</h2>[<a href="/w/index.php?title=Lepton&action=edit&section=2" title="Edit section: History">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Electron#Discovery" title="Electron">Electron § Discovery</a>, <a href="/wiki/Muon#History" title="Muon">Muon § History</a>, and <a href="/wiki/Tau_(particle)#History" title="Tau (particle)">Tau (particle) § History</a></div> <figure class="mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:Feynman_diagram_of_muon_to_electron_decay.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/5/55/Feynman_diagram_of_muon_to_electron_decay.svg/200px-Feynman_diagram_of_muon_to_electron_decay.svg.png" decoding="async" width="200" height="124" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/55/Feynman_diagram_of_muon_to_electron_decay.svg/300px-Feynman_diagram_of_muon_to_electron_decay.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/55/Feynman_diagram_of_muon_to_electron_decay.svg/400px-Feynman_diagram_of_muon_to_electron_decay.svg.png 2x" data-file-width="220" data-file-height="136" /></a><figcaption>A muon transmutes into a <a href="/wiki/Muon_neutrino" title="Muon neutrino">muon neutrino</a> by emitting a <a href="/wiki/W_boson" class="mw-redirect" title="W boson"> W− boson</a>. The W− boson subsequently decays into an <a href="/wiki/Electron" title="Electron">electron</a> and an <a href="/wiki/Electron_antineutrino" class="mw-redirect" title="Electron antineutrino">electron antineutrino</a>.</figcaption></figure> <table class="wikitable" style="float:right; font-size:90%; margin:.5em 0 .5em 1em;"> <caption>Lepton nomenclature </caption> <tbody><tr> <th>Particle name</th> <th>Antiparticle name </th></tr> <tr> <td>electron</td> <td>antielectron positron </td></tr> <tr> <td>electron neutrino</td> <td>electron antineutrino </td></tr> <tr> <td>muon mu lepton mu</td> <td>antimuon antimu lepton antimu </td></tr> <tr> <td>muon neutrino muonic neutrino mu neutrino</td> <td>muon antineutrino muonic antineutrino mu antineutrino </td></tr> <tr> <td>tauon tau lepton tau</td> <td>antitauon antitau lepton antitau </td></tr> <tr> <td>tauon neutrino tauonic neutrino tau neutrino</td> <td>tauon antineutrino tauonic antineutrino tau antineutrino </td></tr></tbody></table> The first lepton identified was the electron, discovered by <a href="/wiki/J.J._Thomson" class="mw-redirect" title="J.J. Thomson">J.J. Thomson</a> and his team of British physicists in 1897.<a href="#cite_note-23">[23]</a><a href="#cite_note-24">[24]</a> Then in 1930, <a href="/wiki/Wolfgang_Pauli" title="Wolfgang Pauli">Wolfgang Pauli</a> postulated the <a href="/wiki/Electron_neutrino" title="Electron neutrino">electron neutrino</a> to preserve <a href="/wiki/Conservation_of_energy" title="Conservation of energy">conservation of energy</a>, <a href="/wiki/Conservation_of_momentum" class="mw-redirect" title="Conservation of momentum">conservation of momentum</a>, and <a href="/wiki/Conservation_of_angular_momentum" class="mw-redirect" title="Conservation of angular momentum">conservation of angular momentum</a> in <a href="/wiki/Beta_decay" title="Beta decay">beta decay</a>.<a href="#cite_note-25">[25]</a> Pauli theorized that an undetected particle was carrying away the difference between the <a href="/wiki/Energy" title="Energy">energy</a>, <a href="/wiki/Momentum" title="Momentum">momentum</a>, and <a href="/wiki/Angular_momentum" title="Angular momentum">angular momentum</a> of the initial and observed final particles. The electron neutrino was simply called the neutrino, as it was not yet known that neutrinos came in different flavours (or different "generations"). Nearly 40 years after the discovery of the electron, the <a href="/wiki/Muon" title="Muon">muon</a> was discovered by <a href="/wiki/Carl_D._Anderson" class="mw-redirect" title="Carl D. Anderson">Carl D. Anderson</a> in 1936. Due to its mass, it was initially categorized as a <a href="/wiki/Meson" title="Meson">meson</a> rather than a lepton.<a href="#cite_note-26">[26]</a> It later became clear that the muon was much more similar to the electron than to mesons, as muons do not undergo the <a href="/wiki/Strong_interaction" title="Strong interaction">strong interaction</a>, and thus the muon was reclassified: electrons, muons, and the (electron) neutrino were grouped into a new group of particles—the leptons. In 1962, <a href="/wiki/Leon_M._Lederman" title="Leon M. Lederman">Leon M. Lederman</a>, <a href="/wiki/Melvin_Schwartz" title="Melvin Schwartz">Melvin Schwartz</a>, and <a href="/wiki/Jack_Steinberger" title="Jack Steinberger">Jack Steinberger</a> showed that more than one type of neutrino exists by first detecting interactions of the <a href="/wiki/Muon" title="Muon">muon</a> neutrino, which earned them the <a href="/wiki/Nobel_Prize_in_Physics" title="Nobel Prize in Physics">1988 Nobel Prize</a>, although by then the different flavours of neutrino had already been theorized.<a href="#cite_note-27">[27]</a> The <a href="/wiki/Tau_(particle)" title="Tau (particle)">tau</a> was first detected in a series of experiments between 1974 and 1977 by <a href="/wiki/Martin_Lewis_Perl" title="Martin Lewis Perl">Martin Lewis Perl</a> with his colleagues at the <a href="/wiki/SLAC" class="mw-redirect" title="SLAC">SLAC</a> <a href="/wiki/Lawrence_Berkeley_National_Laboratory" title="Lawrence Berkeley National Laboratory">LBL group</a>.<a href="#cite_note-28">[28]</a> Like the electron and the muon, it too was expected to have an associated neutrino. The first evidence for tau neutrinos came from the observation of "missing" energy and momentum in tau decay, analogous to the "missing" energy and momentum in beta decay leading to the discovery of the electron neutrino. The first detection of tau neutrino interactions was announced in 2000 by the <a href="/wiki/DONUT" title="DONUT">DONUT</a> collaboration at <a href="/wiki/Fermilab" title="Fermilab">Fermilab</a>, making it the second-to-latest particle of the <a href="/wiki/Standard_Model" title="Standard Model">Standard Model</a> to have been directly observed,<a href="#cite_note-obs-29">[29]</a> with <a href="/wiki/Higgs_boson" title="Higgs boson">Higgs boson</a> being discovered in 2012. Although all present data is consistent with three generations of leptons, some particle physicists are searching for a fourth generation. The current lower limit on the mass of such a fourth charged lepton is 100.8 <a href="/wiki/Electronvolt#Mass" title="Electronvolt">GeV/c2</a>,<a href="#cite_note-30">[30]</a> while its associated neutrino would have a mass of at least 45.0 <a href="/wiki/Electronvolt#Mass" title="Electronvolt">GeV/c2</a>.<a href="#cite_note-31">[31]</a> <div class="mw-heading mw-heading2"><h2 id="Properties">Properties</h2>[<a href="/w/index.php?title=Lepton&action=edit&section=3" title="Edit section: Properties">edit</a>]</div> <div class="mw-heading mw-heading3"><h3 id="Spin_and_chirality">Spin and chirality</h3>[<a href="/w/index.php?title=Lepton&action=edit&section=4" title="Edit section: Spin and chirality">edit</a>]</div> <figure class="mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Right_left_helicity.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a9/Right_left_helicity.svg/250px-Right_left_helicity.svg.png" decoding="async" width="200" height="63" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/a9/Right_left_helicity.svg/330px-Right_left_helicity.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/a9/Right_left_helicity.svg/400px-Right_left_helicity.svg.png 2x" data-file-width="380" data-file-height="120" /></a><figcaption>Left-handed and right-handed helicities</figcaption></figure> Leptons are <a href="/wiki/Spin_(physics)" title="Spin (physics)">spin</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035" />⁠1/2⁠ particles. The <a href="/wiki/Spin-statistics_theorem" class="mw-redirect" title="Spin-statistics theorem">spin-statistics theorem</a> thus implies that they are <a href="/wiki/Fermion" title="Fermion">fermions</a> and thus that they are subject to the <a href="/wiki/Pauli_exclusion_principle" title="Pauli exclusion principle">Pauli exclusion principle</a>: no two leptons of the same species can be in the same state at the same time. Furthermore, it means that a lepton can have only two possible spin states, namely up or down. A closely related property is <a href="/wiki/Chirality_(physics)" title="Chirality (physics)">chirality</a>, which in turn is closely related to a more easily visualized property called <a href="/wiki/Helicity_(particle_physics)" title="Helicity (particle physics)">helicity</a>. The helicity of a particle is the direction of its spin relative to its <a href="/wiki/Momentum" title="Momentum">momentum</a>; particles with spin in the same direction as their momentum are called right-handed and they are otherwise called left-handed. When a particle is massless, the direction of its momentum relative to its spin is the same in every reference frame, whereas for massive particles it is possible to 'overtake' the particle by choosing a faster-moving <a href="/wiki/Lorentz_transformation" title="Lorentz transformation">reference frame</a>; in the faster frame, the helicity is reversed. Chirality is a technical property, defined through transformation behaviour under the <a href="/wiki/Poincar%C3%A9_group" title="Poincaré group">Poincaré group</a>, that does not change with reference frame. It is contrived to agree with helicity for massless particles, and is still well defined for particles with mass. In many <a href="/wiki/Quantum_field_theories" class="mw-redirect" title="Quantum field theories">quantum field theories</a>, such as <a href="/wiki/Quantum_electrodynamics" title="Quantum electrodynamics">quantum electrodynamics</a> and <a href="/wiki/Quantum_chromodynamics" title="Quantum chromodynamics">quantum chromodynamics</a>, left- and right-handed fermions are identical. However, the Standard Model's <a href="/wiki/Weak_interaction" title="Weak interaction">weak interaction</a> treats left-handed and right-handed fermions differently: only left-handed fermions (and right-handed anti-fermions) participate in the weak interaction. This is an example of <a href="/wiki/Parity_violation" class="mw-redirect" title="Parity violation">parity violation</a> explicitly written into the model. In the literature, left-handed fields are often denoted by a capital L subscript (e.g. the normal electron e− L) and right-handed fields are denoted by a capital R subscript (e.g. a positron e+ R). Right-handed neutrinos and left-handed anti-neutrinos have no possible interaction with other particles (see <a href="/wiki/Sterile_neutrino" title="Sterile neutrino">Sterile neutrino</a>) and so are not a functional part of the Standard Model, although their exclusion is not a strict requirement; they are sometimes listed in particle tables to emphasize that they would have no active role if included in the model. Even though electrically charged right-handed particles (electron, muon, or tau) do not engage in the weak interaction specifically, they can still interact electrically, and hence still participate in the <a href="/wiki/Electroweak_unification" class="mw-redirect" title="Electroweak unification">combined electroweak force</a>, although with different strengths (<a href="/wiki/Weak_hypercharge" title="Weak hypercharge">YW</a>). <div style="clear:both;" class=""></div> <div class="mw-heading mw-heading3"><h3 id="Electromagnetic_interaction">Electromagnetic interaction</h3>[<a href="/w/index.php?title=Lepton&action=edit&section=5" title="Edit section: Electromagnetic interaction">edit</a>]</div> <figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Lepton-interaction-vertex-eeg.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/b/b5/Lepton-interaction-vertex-eeg.svg/250px-Lepton-interaction-vertex-eeg.svg.png" decoding="async" width="220" height="154" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/b5/Lepton-interaction-vertex-eeg.svg/330px-Lepton-interaction-vertex-eeg.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/b5/Lepton-interaction-vertex-eeg.svg/440px-Lepton-interaction-vertex-eeg.svg.png 2x" data-file-width="300" data-file-height="210" /></a><figcaption>Lepton–photon interaction</figcaption></figure> One of the most prominent properties of leptons is their <a href="/wiki/Electric_charge" title="Electric charge">electric charge</a>, Q. The electric charge determines the strength of their <a href="/wiki/Electromagnetic_interaction" class="mw-redirect" title="Electromagnetic interaction">electromagnetic interactions</a>. It determines the strength of the <a href="/wiki/Electric_field" title="Electric field">electric field</a> generated by the particle (see <a href="/wiki/Coulomb%27s_law" title="Coulomb's law">Coulomb's law</a>) and how strongly the particle reacts to an external electric or magnetic field (see <a href="/wiki/Lorentz_force" title="Lorentz force">Lorentz force</a>). Each generation contains one lepton with Q = −1 <a href="/wiki/Elementary_charge" title="Elementary charge">e</a> and one lepton with zero electric charge. The lepton with electric charge is commonly simply referred to as a charged lepton while a neutral lepton is called a neutrino. For example, the first generation consists of the electron e− with a negative electric charge and the electrically neutral electron neutrino ν e. In the language of quantum field theory, the electromagnetic interaction of the charged leptons is expressed by the fact that the particles interact with the quantum of the electromagnetic field, the <a href="/wiki/Photon" title="Photon">photon</a>. The <a href="/wiki/Feynman_diagram" title="Feynman diagram">Feynman diagram</a> of the electron–photon interaction is shown on the right. Because leptons possess an intrinsic rotation in the form of their spin, charged leptons generate a magnetic field. The size of their <a href="/wiki/Magnetic_dipole_moment" class="mw-redirect" title="Magnetic dipole moment">magnetic dipole moment</a> μ is given by <dl><dd><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mu =g\,{\frac {\;Q\hbar \;}{4m}}\ ,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>μ</mi> <mo>=</mo> <mi>g</mi> <mspace width="thinmathspace"></mspace> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mspace width="thickmathspace"></mspace> <mi>Q</mi> <mi class="MJX-variant">ℏ</mi> <mspace width="thickmathspace"></mspace> </mrow> <mrow> <mn>4</mn> <mi>m</mi> </mrow> </mfrac> </mrow> <mtext> </mtext> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \mu =g\,{\frac {\;Q\hbar \;}{4m}}\ ,}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/edab31f5d2bb6eb4185c837c62ad3d11b2c3b95a" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.838ex; width:12.502ex; height:5.343ex;" alt="{\displaystyle \mu =g\,{\frac {\;Q\hbar \;}{4m}}\ ,}" /></dd></dl> where m is the mass of the lepton and g is the so-called <a href="/wiki/G-factor_(physics)" title="G-factor (physics)">"g factor"</a> for the lepton. First-order quantum mechanical approximation predicts that the g factor is 2 for all leptons. However, higher-order quantum effects caused by loops in Feynman diagrams introduce corrections to this value. These corrections, referred to as the <a href="/wiki/Anomalous_magnetic_dipole_moment" title="Anomalous magnetic dipole moment">anomalous magnetic dipole moment</a>, are very sensitive to the details of a quantum field theory model, and thus provide the opportunity for precision tests of the Standard Model. The theoretical and measured values for the electron anomalous magnetic dipole moment are within agreement within eight significant figures.<a href="#cite_note-32">[32]</a> The results for the muon, however, <a href="/wiki/Muon_g-2" title="Muon g-2">are problematic</a>, hinting at a small, persistent discrepancy between the Standard Model and experiment. <div class="mw-heading mw-heading3"><h3 id="Weak_interaction">Weak interaction</h3>[<a href="/w/index.php?title=Lepton&action=edit&section=6" title="Edit section: Weak interaction">edit</a>]</div> <table style="float:right; margin: 0em 0em 1em 1em"> <tbody><tr> <td> <table class="wikitable" style="font-size:90%;"> <tbody><tr> <td><a href="/wiki/File:Lepton-interaction-vertex-evW.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/1/1b/Lepton-interaction-vertex-evW.svg/150px-Lepton-interaction-vertex-evW.svg.png" decoding="async" width="150" height="105" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/1b/Lepton-interaction-vertex-evW.svg/225px-Lepton-interaction-vertex-evW.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/1b/Lepton-interaction-vertex-evW.svg/300px-Lepton-interaction-vertex-evW.svg.png 2x" data-file-width="300" data-file-height="210" /></a> </td> <td><a href="/wiki/File:Lepton-interaction-vertex-pvW.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/7/7f/Lepton-interaction-vertex-pvW.svg/150px-Lepton-interaction-vertex-pvW.svg.png" decoding="async" width="150" height="105" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/7f/Lepton-interaction-vertex-pvW.svg/225px-Lepton-interaction-vertex-pvW.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/7/7f/Lepton-interaction-vertex-pvW.svg/300px-Lepton-interaction-vertex-pvW.svg.png 2x" data-file-width="300" data-file-height="210" /></a> </td> <td><a href="/wiki/File:Lepton-interaction-vertex-eeZ.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/4/4b/Lepton-interaction-vertex-eeZ.svg/150px-Lepton-interaction-vertex-eeZ.svg.png" decoding="async" width="150" height="105" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/4/4b/Lepton-interaction-vertex-eeZ.svg/225px-Lepton-interaction-vertex-eeZ.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/4/4b/Lepton-interaction-vertex-eeZ.svg/300px-Lepton-interaction-vertex-eeZ.svg.png 2x" data-file-width="300" data-file-height="210" /></a> </td></tr> <tr> <td colspan="3"><div class="center">The <a href="/wiki/Weak_interaction" title="Weak interaction">weak interactions</a> of the first generation leptons.</div> </td></tr></tbody></table> </td></tr></tbody></table> In the Standard Model, the left-handed charged lepton and the left-handed neutrino are arranged in <a href="/wiki/Doublet_(physics)" class="mw-redirect" title="Doublet (physics)">doublet</a> that transforms in the <a href="/wiki/Spinor" title="Spinor">spinor</a> representation (T = <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035" />⁠ 1 /2⁠) of the <a href="/wiki/Weak_isospin" title="Weak isospin">weak isospin</a> <a href="/wiki/SU(2)" class="mw-redirect" title="SU(2)">SU(2)</a> gauge symmetry. This means that these particles are eigenstates of the isospin projection T3 with eigenvalues <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035" />⁠++ 1 /2⁠ and <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035" />⁠−+ 1 /2⁠ respectively. In the meantime, the right-handed charged lepton transforms as a weak isospin scalar (T = 0) and thus does not participate in the <a href="/wiki/Weak_interaction" title="Weak interaction">weak interaction</a>, while there is no evidence that a right-handed neutrino exists at all. The <a href="/wiki/Higgs_mechanism" title="Higgs mechanism">Higgs mechanism</a> recombines the gauge fields of the weak isospin SU(2) and the <a href="/wiki/Weak_hypercharge" title="Weak hypercharge">weak hypercharge</a> U(1) symmetries to three massive vector bosons ( W+ , W− , Z0 ) mediating the <a href="/wiki/Weak_interaction" title="Weak interaction">weak interaction</a>, and one massless vector boson, the photon (γ), responsible for the electromagnetic interaction. The electric charge Q can be calculated from the isospin projection T3 and weak hypercharge YW through the <a href="/wiki/Gell-Mann%E2%80%93Nishijima_formula" title="Gell-Mann–Nishijima formula">Gell-Mann–Nishijima formula</a>, <dl><dd>Q = T3 + <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035" />⁠ 1 /2⁠ YW.</dd></dl> To recover the observed electric charges for all particles, the left-handed weak isospin doublet (νeL, e− L) must thus have YW = −1, while the right-handed isospin scalar e− R must have YW = −2. The interaction of the leptons with the massive weak interaction vector bosons is shown in the figure on the right. <div class="mw-heading mw-heading3"><h3 id="Mass">Mass</h3>[<a href="/w/index.php?title=Lepton&action=edit&section=7" title="Edit section: Mass">edit</a>]</div> In the <a href="/wiki/Standard_Model" title="Standard Model">Standard Model</a>, each lepton starts out with no intrinsic mass. The charged leptons (i.e. the electron, muon, and tau) obtain an effective mass through interaction with the <a href="/wiki/Higgs_field" class="mw-redirect" title="Higgs field">Higgs field</a>, but the neutrinos remain massless. For technical reasons, the masslessness of the neutrinos implies that there is no mixing of the different generations of charged leptons as <a href="/wiki/CKM_matrix" class="mw-redirect" title="CKM matrix">there is for quarks</a>. The zero mass of neutrino is in close agreement with current direct experimental observations of the mass.<a href="#cite_note-33">[33]</a> However, it is known from indirect experiments—most prominently from observed <a href="/wiki/Neutrino_oscillation" title="Neutrino oscillation">neutrino oscillations</a><a href="#cite_note-34">[34]</a>—that neutrinos have to have a nonzero mass, probably less than 2 <a href="/wiki/Electronvolt#Mass" title="Electronvolt">eV/c2</a>.<a href="#cite_note-Neutrino-35">[35]</a> This implies the existence of physics <a href="/wiki/Beyond_the_Standard_Model" class="mw-redirect" title="Beyond the Standard Model">beyond the Standard Model</a>. The currently most favoured extension is the so-called <a href="/wiki/Seesaw_mechanism" title="Seesaw mechanism">seesaw mechanism</a>, which would explain both why the left-handed neutrinos are so light compared to the corresponding charged leptons, and why we have not yet seen any right-handed neutrinos. <div class="mw-heading mw-heading3"><h3 id="Lepton_flavor_quantum_numbers">Lepton flavor quantum numbers</h3>[<a href="/w/index.php?title=Lepton&action=edit&section=8" title="Edit section: Lepton flavor quantum numbers">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Lepton_number" title="Lepton number">Lepton number</a></div> The members of each generation's <a href="/wiki/Weak_isospin" title="Weak isospin">weak isospin</a> <a href="/wiki/Doublet_(physics)" class="mw-redirect" title="Doublet (physics)">doublet</a> are assigned <a href="/wiki/Lepton_number" title="Lepton number">leptonic numbers</a> that are conserved under the Standard Model.<a href="#cite_note-MartinShaw-36">[36]</a> Electrons and electron neutrinos have an electronic number of Le = 1, while muons and muon neutrinos have a muonic number of Lμ = 1, while tau particles and tau neutrinos have a tauonic number of Lτ = 1. The antileptons have their respective generation's leptonic numbers of −1. Conservation of the leptonic numbers means that the number of leptons of the same type remains the same, when particles interact. This implies that leptons and antileptons must be created in pairs of a single generation. For example, the following processes are allowed under conservation of leptonic numbers: <figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Lepton_isodoublets_fixed.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/9/93/Lepton_isodoublets_fixed.png/250px-Lepton_isodoublets_fixed.png" decoding="async" width="220" height="56" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/9/93/Lepton_isodoublets_fixed.png 1.5x" data-file-width="302" data-file-height="77" /></a><figcaption>Each generation forms a <a href="/wiki/Weak_isospin" title="Weak isospin">weak isospin</a> <a href="/wiki/Doublet_(physics)" class="mw-redirect" title="Doublet (physics)">doublet</a>.</figcaption></figure> <dl><dd><a href="/wiki/Photon" title="Photon"> γ </a>    →   <a href="/wiki/Electron" title="Electron"> e− </a> + <a href="/wiki/Positron" title="Positron"> e+ </a>,</dd> <dd><a href="/wiki/Z_boson" class="mw-redirect" title="Z boson"> Z0 </a>  →   <a href="/wiki/Tau_(particle)" title="Tau (particle)"> τ− </a> + <a href="/wiki/Antitau" class="mw-redirect" title="Antitau"> τ+ </a>,</dd></dl> but none of these: <dl><dd><a href="/wiki/Photon" title="Photon"> γ </a>      →   <a href="/wiki/Electron" title="Electron"> e− </a> + <a href="/wiki/Antimuon" class="mw-redirect" title="Antimuon"> μ+ </a>,</dd> <dd><a href="/wiki/W_boson" class="mw-redirect" title="W boson"> W− </a>  →   <a href="/wiki/Electron" title="Electron"> e− </a> + <a href="/wiki/Tau_neutrino" title="Tau neutrino"> ν τ</a>,</dd> <dd><a href="/wiki/Z_boson" class="mw-redirect" title="Z boson"> Z0 </a>    →   <a href="/wiki/Muon" title="Muon"> μ− </a> + <a href="/wiki/Antitau" class="mw-redirect" title="Antitau"> τ+ </a>.</dd></dl> However, <a href="/wiki/Neutrino_oscillation" title="Neutrino oscillation">neutrino oscillations</a> are known to violate the conservation of the individual leptonic numbers. Such a violation is considered to be smoking gun evidence for <a href="/wiki/Physics_beyond_the_Standard_Model" title="Physics beyond the Standard Model">physics beyond the Standard Model</a>. A much stronger conservation law is the conservation of the total number of leptons (L with no subscript), conserved even in the case of neutrino oscillations, but even it is still violated by a tiny amount by the <a href="/wiki/Chiral_anomaly" title="Chiral anomaly">chiral anomaly</a>. <div class="mw-heading mw-heading2"><h2 id="Universality">Universality</h2>[<a href="/w/index.php?title=Lepton&action=edit&section=9" title="Edit section: Universality">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/LHCb_experiment#Lepton_flavour_universality" title="LHCb experiment">LHCb experiment § Lepton flavour universality</a></div> The coupling of leptons to all types of <a href="/wiki/Gauge_boson" title="Gauge boson">gauge boson</a> are flavour-independent: The interaction between leptons and a gauge boson measures the same for each lepton.<a href="#cite_note-MartinShaw-36">[36]</a> This property is called lepton universality and has been tested in measurements of the <a href="/wiki/Muon" title="Muon">muon</a> and <a href="/wiki/Tau_lepton" class="mw-redirect" title="Tau lepton">tau</a> <a href="/wiki/Mean_lifetime" class="mw-redirect" title="Mean lifetime">lifetimes</a> and of <a href="/wiki/Z_boson" class="mw-redirect" title="Z boson"> Z </a> boson partial <a href="/wiki/Decay_width" class="mw-redirect" title="Decay width">decay widths</a>, particularly at the <a href="/wiki/Stanford_Linear_Collider" class="mw-redirect" title="Stanford Linear Collider">Stanford Linear Collider</a> (SLC) and <a href="/wiki/Large_Electron%E2%80%93Positron_Collider" title="Large Electron–Positron Collider">Large Electron–Positron Collider</a> (LEP) experiments.<a href="#cite_note-Cumalat1993-37">[37]</a>: 241–243 <a href="#cite_note-Fraser1998-38">[38]</a>: 138  The decay rate (<math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \Gamma }"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi mathvariant="normal">Γ</mi> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \Gamma }</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/4cfde86a3f7ec967af9955d0988592f0693d2b19" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.453ex; height:2.176ex;" alt="{\displaystyle \Gamma }" />) of muons through the process <a href="/wiki/Muon" title="Muon"> μ− </a> → <a href="/wiki/Electron" title="Electron"> e− </a> + <a href="/wiki/Electron_antineutrino" class="mw-redirect" title="Electron antineutrino"> ν e</a> + <a href="/wiki/Muon_neutrino" title="Muon neutrino"> ν μ</a> is approximately given by an expression of the form (see <a href="/wiki/Muon_decay" class="mw-redirect" title="Muon decay">muon decay</a> for more details)<a href="#cite_note-MartinShaw-36">[36]</a> <dl><dd><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \Gamma \left(\mu ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\mu }\right)\approx K_{2}\,G_{\text{F}}^{2}\,m_{\mu }^{5}~,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi mathvariant="normal">Γ</mi> <mrow> <mo>(</mo> <mrow> <msup> <mi>μ</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo stretchy="false">→</mo> <msup> <mi>e</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mover> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>e</mi> </mrow> </msub> <mo stretchy="false">¯</mo> </mover> </mrow> </mrow> <mo>+</mo> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>μ</mi> </mrow> </msub> </mrow> <mo>)</mo> </mrow> <mo>≈</mo> <msub> <mi>K</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msub> <mspace width="thinmathspace"></mspace> <msubsup> <mi>G</mi> <mrow class="MJX-TeXAtom-ORD"> <mtext>F</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msubsup> <mspace width="thinmathspace"></mspace> <msubsup> <mi>m</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>μ</mi> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>5</mn> </mrow> </msubsup> <mtext> </mtext> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \Gamma \left(\mu ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\mu }\right)\approx K_{2}\,G_{\text{F}}^{2}\,m_{\mu }^{5}~,}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/79a032c46b4b1ac52b0325b2ca50ab765a1e5afd" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:37.814ex; height:3.176ex;" alt="{\displaystyle \Gamma \left(\mu ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\mu }\right)\approx K_{2}\,G_{\text{F}}^{2}\,m_{\mu }^{5}~,}" /></dd></dl> where K2 is some constant, and GF is the <a href="/wiki/Fermi_coupling_constant" class="mw-redirect" title="Fermi coupling constant">Fermi coupling constant</a>. The decay rate of tau particles through the process <a href="/wiki/Tauon" class="mw-redirect" title="Tauon"> τ− </a> → <a href="/wiki/Electron" title="Electron"> e− </a> + <a href="/wiki/Electron_antineutrino" class="mw-redirect" title="Electron antineutrino"> ν e</a> + <a href="/wiki/Tau_neutrino" title="Tau neutrino"> ν τ</a> is given by an expression of the same form<a href="#cite_note-MartinShaw-36">[36]</a> <dl><dd><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \Gamma \left(\tau ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\tau }\right)\approx K_{3}\,G_{\text{F}}^{2}\,m_{\tau }^{5}~,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi mathvariant="normal">Γ</mi> <mrow> <mo>(</mo> <mrow> <msup> <mi>τ</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo stretchy="false">→</mo> <msup> <mi>e</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mover> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>e</mi> </mrow> </msub> <mo stretchy="false">¯</mo> </mover> </mrow> </mrow> <mo>+</mo> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>τ</mi> </mrow> </msub> </mrow> <mo>)</mo> </mrow> <mo>≈</mo> <msub> <mi>K</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>3</mn> </mrow> </msub> <mspace width="thinmathspace"></mspace> <msubsup> <mi>G</mi> <mrow class="MJX-TeXAtom-ORD"> <mtext>F</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msubsup> <mspace width="thinmathspace"></mspace> <msubsup> <mi>m</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>τ</mi> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>5</mn> </mrow> </msubsup> <mtext> </mtext> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \Gamma \left(\tau ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\tau }\right)\approx K_{3}\,G_{\text{F}}^{2}\,m_{\tau }^{5}~,}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/f85855953a8c9cbab9025617c89f85ef2b30f1f8" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:37.387ex; height:3.176ex;" alt="{\displaystyle \Gamma \left(\tau ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\tau }\right)\approx K_{3}\,G_{\text{F}}^{2}\,m_{\tau }^{5}~,}" /></dd></dl> where K3 is some other constant. Muon–tauon universality implies that K2 ≈ K3. On the other hand, electron–muon universality implies<a href="#cite_note-MartinShaw-36">[36]</a> <dl><dd><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle 0.9726\times \Gamma \left(\tau ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\tau }\right)=\Gamma \left(\tau ^{-}\rightarrow \mu ^{-}+{\bar {\nu _{\mu }}}+\nu _{\tau }\right)~.}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mn>0.9726</mn> <mo>×</mo> <mi mathvariant="normal">Γ</mi> <mrow> <mo>(</mo> <mrow> <msup> <mi>τ</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo stretchy="false">→</mo> <msup> <mi>e</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mover> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>e</mi> </mrow> </msub> <mo stretchy="false">¯</mo> </mover> </mrow> </mrow> <mo>+</mo> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>τ</mi> </mrow> </msub> </mrow> <mo>)</mo> </mrow> <mo>=</mo> <mi mathvariant="normal">Γ</mi> <mrow> <mo>(</mo> <mrow> <msup> <mi>τ</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo stretchy="false">→</mo> <msup> <mi>μ</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mover> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>μ</mi> </mrow> </msub> <mo stretchy="false">¯</mo> </mover> </mrow> </mrow> <mo>+</mo> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>τ</mi> </mrow> </msub> </mrow> <mo>)</mo> </mrow> <mtext> </mtext> <mo>.</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle 0.9726\times \Gamma \left(\tau ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\tau }\right)=\Gamma \left(\tau ^{-}\rightarrow \mu ^{-}+{\bar {\nu _{\mu }}}+\nu _{\tau }\right)~.}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/5c1a78f9c3769f2574568bdcf2de6eaf0a3426f5" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:60.566ex; height:3.176ex;" alt="{\displaystyle 0.9726\times \Gamma \left(\tau ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\tau }\right)=\Gamma \left(\tau ^{-}\rightarrow \mu ^{-}+{\bar {\nu _{\mu }}}+\nu _{\tau }\right)~.}" /></dd></dl> The <a href="/wiki/Branching_ratio" class="mw-redirect" title="Branching ratio">branching ratios</a> for the electronic mode (17.82%) and muonic (17.39%) mode of tau decay are not equal due to the mass difference of the final state leptons.<a href="#cite_note-Tauon-21">[21]</a> Universality also accounts for the ratio of muon and tau lifetimes. The lifetime <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mathrm {T} _{\ell }}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">T</mi> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mi>ℓ</mi> </mrow> </msub> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \mathrm {T} _{\ell }}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/2af28ebfb04ab0210f9d552af5d983225fa571d2" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:2.596ex; height:2.509ex;" alt="{\displaystyle \mathrm {T} _{\ell }}" /> of a lepton <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \ell }"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>ℓ</mi> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \ell }</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/f066e981e530bacc07efc6a10fa82deee985929e" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:0.97ex; height:2.176ex;" alt="{\displaystyle \ell }" /> (with <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \ell }"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>ℓ</mi> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \ell }</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/f066e981e530bacc07efc6a10fa82deee985929e" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:0.97ex; height:2.176ex;" alt="{\displaystyle \ell }" /> = "μ" or "τ") is related to the decay rate by<a href="#cite_note-MartinShaw-36">[36]</a> <dl><dd><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mathrm {T} _{\ell }={\frac {\;{\mathcal {B}}\left(\ell ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\ell }\right)\;}{\Gamma \left(\ell ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\ell }\right)}}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">T</mi> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mi>ℓ</mi> </mrow> </msub> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mspace width="thickmathspace"></mspace> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mi class="MJX-tex-caligraphic" mathvariant="script">B</mi> </mrow> </mrow> <mrow> <mo>(</mo> <mrow> <msup> <mi>ℓ</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo stretchy="false">→</mo> <msup> <mi>e</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mover> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>e</mi> </mrow> </msub> <mo stretchy="false">¯</mo> </mover> </mrow> </mrow> <mo>+</mo> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>ℓ</mi> </mrow> </msub> </mrow> <mo>)</mo> </mrow> <mspace width="thickmathspace"></mspace> </mrow> <mrow> <mi mathvariant="normal">Γ</mi> <mrow> <mo>(</mo> <mrow> <msup> <mi>ℓ</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo stretchy="false">→</mo> <msup> <mi>e</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mover> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>e</mi> </mrow> </msub> <mo stretchy="false">¯</mo> </mover> </mrow> </mrow> <mo>+</mo> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>ℓ</mi> </mrow> </msub> </mrow> <mo>)</mo> </mrow> </mrow> </mfrac> </mrow> <mspace width="thinmathspace"></mspace> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \mathrm {T} _{\ell }={\frac {\;{\mathcal {B}}\left(\ell ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\ell }\right)\;}{\Gamma \left(\ell ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\ell }\right)}}\,}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/fb27b10b99aaa900f0382435e19da22b4c702369" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.671ex; width:30.531ex; height:6.509ex;" alt="{\displaystyle \mathrm {T} _{\ell }={\frac {\;{\mathcal {B}}\left(\ell ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\ell }\right)\;}{\Gamma \left(\ell ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\ell }\right)}}\,}" />,</dd></dl> where <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \;{\mathcal {B}}(x\rightarrow y)\;}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mspace width="thickmathspace"></mspace> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mi class="MJX-tex-caligraphic" mathvariant="script">B</mi> </mrow> </mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">→</mo> <mi>y</mi> <mo stretchy="false">)</mo> <mspace width="thickmathspace"></mspace> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \;{\mathcal {B}}(x\rightarrow y)\;}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/9932d40e9024a4b5d5a62408a8e5698710a2500a" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:10.742ex; height:2.843ex;" alt="{\displaystyle \;{\mathcal {B}}(x\rightarrow y)\;}" /> denotes the branching ratios and <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \;\Gamma (x\rightarrow y)\;}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mspace width="thickmathspace"></mspace> <mi mathvariant="normal">Γ</mi> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">→</mo> <mi>y</mi> <mo stretchy="false">)</mo> <mspace width="thickmathspace"></mspace> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \;\Gamma (x\rightarrow y)\;}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/ef7e518fa3c3e87b137d5c7512d9f0838de19681" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:10.652ex; height:2.843ex;" alt="{\displaystyle \;\Gamma (x\rightarrow y)\;}" /> denotes the <a href="/wiki/Decay_width" class="mw-redirect" title="Decay width">resonance width</a> of the process <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \;x\rightarrow y~,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mspace width="thickmathspace"></mspace> <mi>x</mi> <mo stretchy="false">→</mo> <mi>y</mi> <mtext> </mtext> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \;x\rightarrow y~,}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/c8443db11d7118b95380c2b00ae90059074894f2" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:7.972ex; height:2.176ex;" alt="{\displaystyle \;x\rightarrow y~,}" /> with x and y replaced by two different particles from "e" or "μ" or "τ". The ratio of tau and muon lifetime is thus given by<a href="#cite_note-MartinShaw-36">[36]</a> <dl><dd><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\frac {\,\mathrm {T} _{\tau }\,}{\mathrm {T} _{\mu }}}={\frac {\;{\mathcal {B}}\left(\tau ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\tau }\right)\;}{{\mathcal {B}}\left(\mu ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\mu }\right)}}\,\left({\frac {m_{\mu }}{m_{\tau }}}\right)^{5}~.}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mspace width="thinmathspace"></mspace> <msub> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">T</mi> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mi>τ</mi> </mrow> </msub> <mspace width="thinmathspace"></mspace> </mrow> <msub> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">T</mi> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mi>μ</mi> </mrow> </msub> </mfrac> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mspace width="thickmathspace"></mspace> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mi class="MJX-tex-caligraphic" mathvariant="script">B</mi> </mrow> </mrow> <mrow> <mo>(</mo> <mrow> <msup> <mi>τ</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo stretchy="false">→</mo> <msup> <mi>e</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mover> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>e</mi> </mrow> </msub> <mo stretchy="false">¯</mo> </mover> </mrow> </mrow> <mo>+</mo> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>τ</mi> </mrow> </msub> </mrow> <mo>)</mo> </mrow> <mspace width="thickmathspace"></mspace> </mrow> <mrow> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mi class="MJX-tex-caligraphic" mathvariant="script">B</mi> </mrow> </mrow> <mrow> <mo>(</mo> <mrow> <msup> <mi>μ</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo stretchy="false">→</mo> <msup> <mi>e</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>−</mo> </mrow> </msup> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mover> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>e</mi> </mrow> </msub> <mo stretchy="false">¯</mo> </mover> </mrow> </mrow> <mo>+</mo> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>μ</mi> </mrow> </msub> </mrow> <mo>)</mo> </mrow> </mrow> </mfrac> </mrow> <mspace width="thinmathspace"></mspace> <msup> <mrow> <mo>(</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <msub> <mi>m</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>μ</mi> </mrow> </msub> <msub> <mi>m</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>τ</mi> </mrow> </msub> </mfrac> </mrow> <mo>)</mo> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>5</mn> </mrow> </msup> <mtext> </mtext> <mo>.</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\frac {\,\mathrm {T} _{\tau }\,}{\mathrm {T} _{\mu }}}={\frac {\;{\mathcal {B}}\left(\tau ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\tau }\right)\;}{{\mathcal {B}}\left(\mu ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\mu }\right)}}\,\left({\frac {m_{\mu }}{m_{\tau }}}\right)^{5}~.}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/4c6c3a7ab8b71291652bc46a3a6ea7b5c7348a64" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.671ex; width:42.561ex; height:6.676ex;" alt="{\displaystyle {\frac {\,\mathrm {T} _{\tau }\,}{\mathrm {T} _{\mu }}}={\frac {\;{\mathcal {B}}\left(\tau ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\tau }\right)\;}{{\mathcal {B}}\left(\mu ^{-}\rightarrow e^{-}+{\bar {\nu _{e}}}+\nu _{\mu }\right)}}\,\left({\frac {m_{\mu }}{m_{\tau }}}\right)^{5}~.}" /></dd></dl> Using values from the 2008 <a href="/wiki/Review_of_Particle_Physics" class="mw-redirect" title="Review of Particle Physics">Review of Particle Physics</a> for the branching ratios of the muon<a href="#cite_note-Muon-19">[19]</a> and tau<a href="#cite_note-Tauon-21">[21]</a> yields a lifetime ratio of ~ 1.29×10−7, comparable to the measured lifetime ratio of ~ 1.32×10−7. The difference is due to K2 and K3 not actually being constants: They depend slightly on the mass of leptons involved. Recent tests of lepton universality in <a href="/wiki/B_meson" title="B meson"> B meson</a> decays, performed by the <a href="/wiki/LHCb" class="mw-redirect" title="LHCb">LHCb</a>, <a href="/wiki/BaBar_experiment" title="BaBar experiment">BaBar</a>, and <a href="/wiki/Belle_experiment" title="Belle experiment">Belle</a> experiments, have shown consistent deviations from the Standard Model predictions. However the combined statistical and systematic significance is not yet high enough to claim an observation of <a href="/wiki/New_physics" class="mw-redirect" title="New physics">new physics</a>.<a href="#cite_note-Ciezarek2017-39">[39]</a> In July 2021 results on lepton flavour universality have been published testing W decays, previous measurements by the LEP had given a slight imbalance but the new measurement by the <a href="/wiki/ATLAS_experiment" title="ATLAS experiment">ATLAS</a> collaboration have twice the precision and give a ratio of <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle R_{W}^{\tau /\mu }={\mathcal {B}}(W\rightarrow \tau \nu _{\tau })/{\mathcal {B}}(W\rightarrow \mu \nu _{\mu })=0.992\pm 0.013}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msubsup> <mi>R</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>W</mi> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mi>τ</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <mi>μ</mi> </mrow> </msubsup> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mi class="MJX-tex-caligraphic" mathvariant="script">B</mi> </mrow> </mrow> <mo stretchy="false">(</mo> <mi>W</mi> <mo stretchy="false">→</mo> <mi>τ</mi> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>τ</mi> </mrow> </msub> <mo stretchy="false">)</mo> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mi class="MJX-tex-caligraphic" mathvariant="script">B</mi> </mrow> </mrow> <mo stretchy="false">(</mo> <mi>W</mi> <mo stretchy="false">→</mo> <mi>μ</mi> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>μ</mi> </mrow> </msub> <mo stretchy="false">)</mo> <mo>=</mo> <mn>0.992</mn> <mo>±</mo> <mn>0.013</mn> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle R_{W}^{\tau /\mu }={\mathcal {B}}(W\rightarrow \tau \nu _{\tau })/{\mathcal {B}}(W\rightarrow \mu \nu _{\mu })=0.992\pm 0.013}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/8d2d92cd53f37c203e557a425c895dc9652bb555" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:51.463ex; height:3.676ex;" alt="{\displaystyle R_{W}^{\tau /\mu }={\mathcal {B}}(W\rightarrow \tau \nu _{\tau })/{\mathcal {B}}(W\rightarrow \mu \nu _{\mu })=0.992\pm 0.013}" />, which agrees with the standard-model prediction of unity.<a href="#cite_note-40">[40]</a><a href="#cite_note-41">[41]</a><a href="#cite_note-42">[42]</a> In 2024 a preprint by the ATLAS collaboration has published a new value of <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle R_{W}^{\mu /e}={\mathcal {B}}(W\rightarrow \mu \nu _{\mu })/{\mathcal {B}}(W\rightarrow e\nu _{e})=0.9995\pm 0.0045}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msubsup> <mi>R</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>W</mi> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mi>μ</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <mi>e</mi> </mrow> </msubsup> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mi class="MJX-tex-caligraphic" mathvariant="script">B</mi> </mrow> </mrow> <mo stretchy="false">(</mo> <mi>W</mi> <mo stretchy="false">→</mo> <mi>μ</mi> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>μ</mi> </mrow> </msub> <mo stretchy="false">)</mo> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mi class="MJX-tex-caligraphic" mathvariant="script">B</mi> </mrow> </mrow> <mo stretchy="false">(</mo> <mi>W</mi> <mo stretchy="false">→</mo> <mi>e</mi> <msub> <mi>ν</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>e</mi> </mrow> </msub> <mo stretchy="false">)</mo> <mo>=</mo> <mn>0.9995</mn> <mo>±</mo> <mn>0.0045</mn> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle R_{W}^{\mu /e}={\mathcal {B}}(W\rightarrow \mu \nu _{\mu })/{\mathcal {B}}(W\rightarrow e\nu _{e})=0.9995\pm 0.0045}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/8107fe46774815db9b29cc417eabd8608014d2e1" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:53.501ex; height:3.676ex;" alt="{\displaystyle R_{W}^{\mu /e}={\mathcal {B}}(W\rightarrow \mu \nu _{\mu })/{\mathcal {B}}(W\rightarrow e\nu _{e})=0.9995\pm 0.0045}" /> the most precise ratio so far testing the lepton flavour universality.<a href="#cite_note-43">[43]</a><a href="#cite_note-44">[44]</a> <div class="mw-heading mw-heading2"><h2 id="Table_of_leptons">Table of leptons</h2>[<a href="/w/index.php?title=Lepton&action=edit&section=10" title="Edit section: Table of leptons">edit</a>]</div> <dl><dd><table class="wikitable" style="text-align:center"> <caption>Properties of leptons </caption> <tbody><tr> <th rowspan="2"><a href="/wiki/Spin_(physics)" title="Spin (physics)">Spin J</a> [<a href="/wiki/Reduced_Planck_constant" class="mw-redirect" title="Reduced Planck constant">ħ</a>] </th> <th rowspan="2">Particle or antiparticle name </th> <th rowspan="2">Symbol </th> <th rowspan="2"><a href="/wiki/Electric_charge" title="Electric charge">Charge Q</a> [<a href="/wiki/Elementary_charge" title="Elementary charge">e</a>] </th> <th colspan="3">Lepton flavor number </th> <th rowspan="2">Mass [<a href="/wiki/MeV" class="mw-redirect" title="MeV">MeV</a>/c2] </th> <th rowspan="2">Lifetime [<a href="/wiki/Second" title="Second">s</a>] </th></tr> <tr> <th>Le </th> <th>Lμ </th> <th>Lτ </th></tr> <tr> <td rowspan="13"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035" />⁠1/2⁠ </td> <td style="text-align:left"><a href="/wiki/Electron" title="Electron">electron</a><a href="#cite_note-Electron-18">[18]</a> </td> <td><a href="/wiki/Electron" title="Electron"> e− </a> </td> <td>−1 </td> <td>+1 </td> <td rowspan="2">0 </td> <td rowspan="2">0 </td> <td rowspan="2" style="text-align:right">0.510998910(13) </td> <td rowspan="2">stable </td></tr> <tr> <td style="text-align:left"><a href="/wiki/Positron" title="Positron">positron</a><a href="#cite_note-Electron-18">[18]</a> </td> <td><a href="/wiki/Positron" title="Positron"> e+ </a> </td> <td>+1 </td> <td>−1 </td></tr> <tr> <td style="text-align:left"><a href="/wiki/Muon" title="Muon">muon</a><a href="#cite_note-Muon-19">[19]</a> </td> <td><a href="/wiki/Muon" title="Muon"> μ− </a> </td> <td>−1 </td> <td rowspan="2">0 </td> <td>+1 </td> <td rowspan="2">0 </td> <td rowspan="2" style="text-align:right">105.6583668(38) </td> <td rowspan="2" style="text-align:right">2.197019(21)×10−6          </td></tr> <tr> <td style="text-align:left"><a href="/wiki/Antimuon" class="mw-redirect" title="Antimuon">antimuon</a><a href="#cite_note-Muon-19">[19]</a> </td> <td><a href="/wiki/Antimuon" class="mw-redirect" title="Antimuon"> μ+ </a> </td> <td>+1 </td> <td>−1 </td></tr> <tr> <td style="text-align:left"><a href="/wiki/Tau_(particle)" title="Tau (particle)">tau</a><a href="#cite_note-Tauon-21">[21]</a> </td> <td><a href="/wiki/Tau_(particle)" title="Tau (particle)"> τ− </a> </td> <td>−1 </td> <td rowspan="2">0 </td> <td rowspan="2">0 </td> <td>+1 </td> <td rowspan="2" style="text-align:right">1776.84(17) </td> <td rowspan="2" style="text-align:right">2.906(10)×10−13 </td></tr> <tr> <td style="text-align:left"><a href="/wiki/Antitau" class="mw-redirect" title="Antitau">antitau</a><a href="#cite_note-Tauon-21">[21]</a> </td> <td><a href="/wiki/Antitau" class="mw-redirect" title="Antitau"> τ+ </a> </td> <td>+1 </td> <td>−1 </td></tr> <tr> <th colspan="8"> </th></tr> <tr> <td style="text-align:left"><a href="/wiki/Electron_neutrino" title="Electron neutrino">electron neutrino</a><a href="#cite_note-Neutrino-35">[35]</a> </td> <td><a href="/wiki/Electron_neutrino" title="Electron neutrino"> ν e</a> </td> <td rowspan="6">0 </td> <td>+1 </td> <td rowspan="2">0 </td> <td rowspan="2">0 </td> <td rowspan="2" style="text-align:left">< 0.0000022<a href="#cite_note-PeltoniemiSarkamo2005-45">[45]</a> </td> <td rowspan="2">unknown </td></tr> <tr> <td style="text-align:left"><a href="/wiki/Electron_antineutrino" class="mw-redirect" title="Electron antineutrino">electron antineutrino</a> </td> <td><a href="/wiki/Electron_antineutrino" class="mw-redirect" title="Electron antineutrino"> ν e</a> </td> <td>−1 </td></tr> <tr> <td style="text-align:left"><a href="/wiki/Muon_neutrino" title="Muon neutrino">muon neutrino</a><a href="#cite_note-Neutrino-35">[35]</a> </td> <td><a href="/wiki/Muon_neutrino" title="Muon neutrino"> ν μ</a> </td> <td rowspan="2">0 </td> <td>+1 </td> <td rowspan="2">0 </td> <td rowspan="2" style="text-align:left">< 0.17<a href="#cite_note-PeltoniemiSarkamo2005-45">[45]</a> </td> <td rowspan="2">unknown </td></tr> <tr> <td style="text-align:left"><a href="/wiki/Muon_antineutrino" class="mw-redirect" title="Muon antineutrino">muon antineutrino</a><a href="#cite_note-Neutrino-35">[35]</a> </td> <td> <a href="/wiki/Muon_antineutrino" class="mw-redirect" title="Muon antineutrino"> ν μ</a> </td> <td>−1 </td></tr> <tr> <td style="text-align:left"><a href="/wiki/Tau_neutrino" title="Tau neutrino">tau neutrino</a><a href="#cite_note-Neutrino-35">[35]</a> </td> <td> <a href="/wiki/Tau_neutrino" title="Tau neutrino"> ν τ</a> </td> <td rowspan="2">0 </td> <td rowspan="2">0 </td> <td>+1 </td> <td rowspan="2" style="text-align:left">< 15.5<a href="#cite_note-PeltoniemiSarkamo2005-45">[45]</a> </td> <td rowspan="2">unknown </td></tr> <tr> <td style="text-align:left"><a href="/wiki/Tau_antineutrino" class="mw-redirect" title="Tau antineutrino">tau antineutrino</a><a href="#cite_note-Neutrino-35">[35]</a> </td> <td> <a href="/wiki/Tauon_antineutrino" class="mw-redirect" title="Tauon antineutrino"> ν τ</a> </td> <td>−1 </td></tr> </tbody></table></dd></dl> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2>[<a href="/w/index.php?title=Lepton&action=edit&section=11" title="Edit section: See also">edit</a>]</div> <ul><li><a href="/wiki/Koide_formula" title="Koide formula">Koide formula</a></li> <li><a href="/wiki/List_of_particles" title="List of particles">List of particles</a></li> <li><a href="/wiki/Preon" title="Preon">Preons</a> – hypothetical particles that were once postulated to be subcomponents of quarks and leptons</li></ul> <div class="mw-heading mw-heading2"><h2 id="Notes">Notes</h2>[<a href="/w/index.php?title=Lepton&action=edit&section=12" title="Edit section: Notes">edit</a>]</div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist reflist-lower-alpha"> </div> <div class="mw-heading mw-heading2"><h2 id="References">References</h2>[<a href="/w/index.php?title=Lepton&action=edit&section=13" title="Edit section: References">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239543626" /><div class="reflist reflist-columns references-column-width" style="column-width: 25em;"> <ol class="references"> <li id="cite_note-1"><a href="#cite_ref-1">^</a> <style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output 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(2003). <a rel="nofollow" class="external text" href="https://archive.org/details/discoveryofsubat00wein_0">The Discovery of Subatomic Particles</a>. <a href="/wiki/Cambridge_University_Press" title="Cambridge University Press">Cambridge University Press</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-521-82351-7" title="Special:BookSources/978-0-521-82351-7"><bdi>978-0-521-82351-7</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+Discovery+of+Subatomic+Particles&rft.pub=Cambridge+University+Press&rft.date=2003&rft.isbn=978-0-521-82351-7&rft.aulast=Weinberg&rft.aufirst=S.&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Fdiscoveryofsubat00wein_0&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALepton" class="Z3988"></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFWilson1997" class="citation book cs1">Wilson, R. (1997). Astronomy Through the Ages: The Story of the Human Attempt to Understand the Universe. <a href="/wiki/CRC_Press" title="CRC Press">CRC Press</a>. p. 138. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-7484-0748-4" title="Special:BookSources/978-0-7484-0748-4"><bdi>978-0-7484-0748-4</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Astronomy+Through+the+Ages%3A+The+Story+of+the+Human+Attempt+to+Understand+the+Universe&rft.pages=138&rft.pub=CRC+Press&rft.date=1997&rft.isbn=978-0-7484-0748-4&rft.aulast=Wilson&rft.aufirst=R.&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALepton" class="Z3988"></li></ul> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2>[<a href="/w/index.php?title=Lepton&action=edit&section=15" title="Edit section: External links">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1235681985" /><style data-mw-deduplicate="TemplateStyles:r1237033735">@media print{body.ns-0 .mw-parser-output .sistersitebox{display:none!important}}@media screen{html.skin-theme-clientpref-night .mw-parser-output .sistersitebox img[src*="Wiktionary-logo-en-v2.svg"]{background-color:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .sistersitebox img[src*="Wiktionary-logo-en-v2.svg"]{background-color:white}}</style><div class="side-box side-box-right plainlinks sistersitebox"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409" /> <div class="side-box-flex"> <div class="side-box-image"><a href="/wiki/File:Commons-logo.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/40px-Commons-logo.svg.png" decoding="async" width="30" height="40" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/60px-Commons-logo.svg.png 1.5x" data-file-width="1024" data-file-height="1376" /></a></div> <div class="side-box-text plainlist">Wikimedia Commons has media related to <a href="https://commons.wikimedia.org/wiki/Category:Leptons" class="extiw" title="commons:Category:Leptons">Leptons</a>.</div></div> </div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1235681985" /><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1237033735" /><div class="side-box side-box-right plainlinks sistersitebox"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409" /> <div class="side-box-flex"> <div class="side-box-image"><a href="/wiki/File:Wiktionary-logo-en-v2.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/9/99/Wiktionary-logo-en-v2.svg/40px-Wiktionary-logo-en-v2.svg.png" decoding="async" width="40" height="40" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/99/Wiktionary-logo-en-v2.svg/60px-Wiktionary-logo-en-v2.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/99/Wiktionary-logo-en-v2.svg/80px-Wiktionary-logo-en-v2.svg.png 2x" data-file-width="512" data-file-height="512" /></a></div> <div class="side-box-text plainlist">Look up <a href="https://en.wiktionary.org/wiki/lepton" class="extiw" title="wiktionary:lepton">lepton</a> in Wiktionary, the free dictionary.</div></div> </div> <ul><li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://pdg.lbl.gov">"Particle Data Group homepage"</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Particle+Data+Group+homepage&rft_id=http%3A%2F%2Fpdg.lbl.gov&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALepton" class="Z3988"> – The PDG compiles authoritative information on particle properties.</li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://hyperphysics.phy-astr.gsu.edu/hbase/particles/lepton.html">"Leptons"</a>. Physics & Astronomy. Georgia State University. <a href="/wiki/Hyperphysics" class="mw-redirect" title="Hyperphysics">Hyperphysics</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Leptons&rft.pub=Georgia+State+University&rft_id=http%3A%2F%2Fhyperphysics.phy-astr.gsu.edu%2Fhbase%2Fparticles%2Flepton.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALepton" class="Z3988"> – a summary of leptons.</li></ul> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist 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navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="/wiki/Quark" title="Quark">Quarks</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Up_quark" title="Up quark">Up (quark</a></li> <li><a href="/wiki/Up_antiquark" class="mw-redirect" title="Up antiquark">antiquark)</a></li> <li><a href="/wiki/Down_quark" title="Down quark">Down (quark</a></li> <li><a href="/wiki/Down_antiquark" class="mw-redirect" title="Down antiquark">antiquark)</a></li> <li><a href="/wiki/Charm_quark" title="Charm quark">Charm (quark</a></li> <li><a href="/wiki/Charm_antiquark" class="mw-redirect" title="Charm antiquark">antiquark)</a></li> <li><a href="/wiki/Strange_quark" title="Strange quark">Strange (quark</a></li> <li><a href="/wiki/Strange_antiquark" class="mw-redirect" title="Strange antiquark">antiquark)</a></li> <li><a href="/wiki/Top_quark" title="Top quark">Top (quark</a></li> <li><a href="/wiki/Top_antiquark" class="mw-redirect" title="Top antiquark">antiquark)</a></li> <li><a href="/wiki/Bottom_quark" title="Bottom quark">Bottom (quark</a></li> <li><a href="/wiki/Bottom_antiquark" class="mw-redirect" title="Bottom antiquark">antiquark)</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a class="mw-selflink selflink">Leptons</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Electron" title="Electron">Electron</a></li> <li><a href="/wiki/Positron" title="Positron">Positron</a></li> <li><a href="/wiki/Muon" title="Muon">Muon</a></li> <li><a href="/wiki/Muon" title="Muon">Antimuon</a></li> <li><a href="/wiki/Tau_(particle)" title="Tau (particle)">Tau</a></li> <li><a href="/wiki/Tau_(particle)" title="Tau (particle)">Antitau</a></li> <li><a href="/wiki/Neutrino" title="Neutrino">Neutrino</a> <ul><li><a href="/wiki/Electron_neutrino" title="Electron neutrino">Electron neutrino</a></li> <li><a href="/wiki/Neutrino#Antineutrinos" title="Neutrino">Electron antineutrino</a></li> <li><a href="/wiki/Muon_neutrino" title="Muon neutrino">Muon neutrino</a></li> <li><a href="/wiki/Neutrino#Antineutrinos" title="Neutrino">Muon antineutrino</a></li> <li><a href="/wiki/Tau_neutrino" title="Tau neutrino">Tau neutrino</a></li> <li><a href="/wiki/Neutrino#Antineutrinos" title="Neutrino">Tau antineutrino</a></li></ul></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align: center;"><a href="/wiki/Boson" title="Boson">Bosons</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:4em;font-weight:normal; text-align: center;"><a href="/wiki/Gauge_boson" title="Gauge boson">Gauge</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Photon" title="Photon">Photon</a></li> <li><a href="/wiki/Gluon" title="Gluon">Gluon</a></li> <li><a href="/wiki/W_and_Z_bosons" title="W and Z bosons">W and Z bosons</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:4em;font-weight:normal; text-align: center;"><a href="/wiki/Scalar_boson" title="Scalar boson">Scalar</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Higgs_boson" title="Higgs boson">Higgs boson </a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align: center;;font-weight:normal; text-align: center;"><a href="/wiki/Ghost_(physics)" title="Ghost (physics)">Ghost fields</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Faddeev%E2%80%93Popov_ghost" title="Faddeev–Popov ghost">Faddeev–Popov ghosts</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align: center;"><a href="/wiki/List_of_hypothetical_particles" title="List of hypothetical particles">Hypothetical</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal; text-align: center;"><a href="/wiki/Superpartner" title="Superpartner">Superpartners</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal; text-align: center;"><a href="/wiki/Gaugino" title="Gaugino">Gauginos</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Gluino" title="Gluino">Gluino</a></li> <li><a href="/wiki/Gravitino" title="Gravitino">Gravitino</a></li> <li><a href="/wiki/Photino" title="Photino">Photino</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal; text-align: center;">Others</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Axino" title="Axino">Axino</a></li> <li><a href="/wiki/Chargino" title="Chargino">Chargino</a></li> <li><a href="/wiki/Higgsino" title="Higgsino">Higgsino</a></li> <li><a href="/wiki/Neutralino" title="Neutralino">Neutralino</a></li> <li><a href="/wiki/Sfermion" title="Sfermion">Sfermion</a> (<a href="/wiki/Stop_squark" title="Stop squark">Stop squark</a>)</li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal; text-align: center;">Others</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Axion" title="Axion">Axion</a></li> <li><a href="/wiki/Curvaton" title="Curvaton">Curvaton</a></li> <li><a href="/wiki/Dilaton" title="Dilaton">Dilaton</a></li> <li><a href="/wiki/Dual_graviton" title="Dual graviton">Dual graviton</a></li> <li><a href="/wiki/Graviphoton" title="Graviphoton">Graviphoton</a></li> <li><a href="/wiki/Graviton" title="Graviton">Graviton</a></li> <li><a href="/wiki/Inflaton" title="Inflaton">Inflaton</a></li> <li><a href="/wiki/Leptoquark" title="Leptoquark">Leptoquark</a></li> <li><a href="/wiki/Magnetic_monopole" title="Magnetic monopole">Magnetic monopole</a></li> <li><a href="/wiki/Majoron" title="Majoron">Majoron</a></li> <li><a href="/wiki/Majorana_fermion" title="Majorana fermion">Majorana fermion</a></li> <li><a href="/wiki/Dark_photon" title="Dark photon">Dark photon</a></li> <li><a href="/wiki/Preon" title="Preon">Preon</a></li> <li><a href="/wiki/Sterile_neutrino" title="Sterile neutrino">Sterile neutrino</a></li> <li><a href="/wiki/Tachyon" title="Tachyon">Tachyon</a></li> <li><a href="/wiki/W%E2%80%B2_and_Z%E2%80%B2_bosons" title="W′ and Z′ bosons">W′ and Z′ bosons</a></li> <li><a href="/wiki/X_and_Y_bosons" title="X and Y bosons">X and Y bosons</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%"><a href="/wiki/Bound_state" title="Bound state">Composite</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th id="Hadrons64" scope="row" class="navbox-group" style="width:1%;text-align: center;"><a href="/wiki/Hadron" title="Hadron">Hadrons</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal; text-align: center;"><a href="/wiki/Baryon" title="Baryon">Baryons</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Nucleon" title="Nucleon">Nucleon</a> <ul><li><a href="/wiki/Proton" title="Proton">Proton</a></li> <li><a href="/wiki/Antiproton" title="Antiproton">Antiproton</a></li> <li><a href="/wiki/Neutron" title="Neutron">Neutron</a></li> <li><a href="/wiki/Antineutron" title="Antineutron">Antineutron</a></li></ul></li> <li><a href="/wiki/Delta_baryon" title="Delta baryon">Delta baryon</a></li> <li><a href="/wiki/Lambda_baryon" title="Lambda baryon">Lambda baryon</a></li> <li><a href="/wiki/Sigma_baryon" title="Sigma baryon">Sigma baryon</a></li> <li><a href="/wiki/Xi_baryon" title="Xi baryon">Xi baryon</a></li> <li><a href="/wiki/Omega_baryon" title="Omega baryon">Omega baryon</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal; text-align: center;"><a href="/wiki/Meson" title="Meson">Mesons</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Pion" title="Pion">Pion</a></li> <li><a href="/wiki/Rho_meson" title="Rho meson">Rho meson</a></li> <li><a href="/wiki/Eta_meson" class="mw-redirect" title="Eta meson">Eta and eta prime mesons</a></li> <li><a href="/wiki/Bottom_eta_meson" title="Bottom eta meson">Bottom eta meson</a></li> <li><a href="/wiki/Phi_meson" title="Phi meson">Phi meson</a></li> <li><a href="/wiki/J/psi_meson" title="J/psi meson">J/psi meson</a></li> <li><a href="/wiki/Omega_meson" title="Omega meson">Omega meson</a></li> <li><a href="/wiki/Upsilon_meson" title="Upsilon meson">Upsilon meson</a></li> <li><a href="/wiki/Kaon" title="Kaon">Kaon</a></li> <li><a href="/wiki/B_meson" title="B meson">B meson</a></li> <li><a href="/wiki/D_meson" title="D meson">D meson</a></li> <li><a href="/wiki/Quarkonium" title="Quarkonium">Quarkonium</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal; text-align: center;"><a href="/wiki/Exotic_hadron" title="Exotic hadron">Exotic hadrons</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Tetraquark" title="Tetraquark">Tetraquark</a> (<a href="/wiki/Double-charm_tetraquark" title="Double-charm tetraquark">Double-charm tetraquark</a>)</li> <li><a href="/wiki/Pentaquark" title="Pentaquark">Pentaquark</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align: center;;font-weight:normal; text-align: center;">Others</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Atomic_nucleus" title="Atomic nucleus">Atomic nuclei</a></li> <li><a href="/wiki/Atom" title="Atom">Atoms</a></li> <li><a href="/wiki/Exotic_atom" title="Exotic atom">Exotic atoms</a> <ul><li><a href="/wiki/Positronium" title="Positronium">Positronium</a></li> <li><a href="/wiki/Muonium" title="Muonium">Muonium</a></li> <li><a href="/wiki/Tauonium" class="mw-redirect" title="Tauonium">Tauonium</a></li> <li><a href="/wiki/Onium" title="Onium">Onia</a></li> <li><a href="/wiki/Pionium" title="Pionium">Pionium</a></li> <li><a href="/wiki/Protonium" title="Protonium">Protonium</a></li></ul></li> <li><a href="/wiki/Superatom" title="Superatom">Superatoms</a></li> <li><a href="/wiki/Molecule" title="Molecule">Molecules</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align: center;"><a href="/wiki/List_of_hypothetical_particles" title="List of hypothetical particles">Hypothetical</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;">Baryons</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Hexaquark" title="Hexaquark">Hexaquark</a></li> <li><a href="/wiki/Heptaquark" title="Heptaquark">Heptaquark</a></li> <li><a href="/wiki/Skyrmion" title="Skyrmion">Skyrmion</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;">Mesons</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Glueball" title="Glueball">Glueball</a></li> <li><a href="/wiki/Theta_meson" title="Theta meson">Theta meson</a></li> <li><a href="/wiki/T_meson" title="T meson">T meson</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal; text-align: center;;font-weight:normal; text-align: center;">Others</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Mesonic_molecule" title="Mesonic molecule">Mesonic molecule</a></li> <li><a href="/wiki/Pomeron" title="Pomeron">Pomeron</a></li> <li><a href="/wiki/Diquark" title="Diquark">Diquark</a></li> <li><a href="/wiki/R-hadron" title="R-hadron">R-hadron</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%"><a href="/wiki/Quasiparticle" title="Quasiparticle">Quasiparticles</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Anyon" title="Anyon">Anyon</a></li> <li><a href="/wiki/Davydov_soliton" title="Davydov soliton">Davydov soliton</a></li> <li><a href="/wiki/Dropleton" title="Dropleton">Dropleton</a></li> <li><a href="/wiki/Exciton" title="Exciton">Exciton</a></li> <li><a href="/wiki/Fracton_(subdimensional_particle)" title="Fracton (subdimensional particle)">Fracton</a></li> <li><a href="/wiki/Electron_hole" title="Electron hole">Hole</a></li> <li><a href="/wiki/Magnon" title="Magnon">Magnon</a></li> <li><a href="/wiki/Phonon" title="Phonon">Phonon</a></li> <li><a href="/wiki/Plasmaron" title="Plasmaron">Plasmaron</a></li> <li><a href="/wiki/Plasmon" title="Plasmon">Plasmon</a></li> <li><a href="/wiki/Polariton" title="Polariton">Polariton</a></li> <li><a href="/wiki/Polaron" title="Polaron">Polaron</a></li> <li><a href="/wiki/Roton" title="Roton">Roton</a></li> <li><a href="/wiki/Trion_(physics)" title="Trion (physics)">Trion</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%">Lists</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/List_of_baryons" title="List of baryons">Baryons</a></li> <li><a href="/wiki/List_of_mesons" title="List of mesons">Mesons</a></li> <li><a href="/wiki/List_of_particles" title="List of particles">Particles</a></li> <li><a href="/wiki/List_of_quasiparticles" title="List of quasiparticles">Quasiparticles</a></li> <li><a href="/wiki/Timeline_of_particle_discoveries" title="Timeline of particle discoveries">Timeline of particle discoveries</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%">Related</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/History_of_subatomic_physics" title="History of subatomic physics">History of subatomic physics</a> <ul><li><a href="/wiki/Timeline_of_atomic_and_subatomic_physics" title="Timeline of atomic and subatomic physics">timeline</a></li></ul></li> <li><a href="/wiki/Standard_Model" title="Standard Model">Standard Model</a> <ul><li><a href="/wiki/Mathematical_formulation_of_the_Standard_Model" title="Mathematical formulation of the Standard Model">mathematical formulation</a></li></ul></li> <li><a href="/wiki/Subatomic_particle" title="Subatomic particle">Subatomic particles</a></li> <li><a href="/wiki/Particle" title="Particle">Particles</a></li> <li><a href="/wiki/Antiparticle" title="Antiparticle">Antiparticles</a></li> <li><a href="/wiki/Nuclear_physics" title="Nuclear physics">Nuclear physics</a></li> <li><a href="/wiki/Eightfold_way_(physics)" title="Eightfold way (physics)">Eightfold way</a> <ul><li><a href="/wiki/Quark_model" title="Quark model">Quark model</a></li></ul></li> <li><a href="/wiki/Exotic_matter" title="Exotic matter">Exotic matter</a></li> <li><a href="/wiki/Massless_particle" title="Massless particle">Massless particle</a></li> <li><a href="/wiki/Relativistic_particle" title="Relativistic particle">Relativistic particle</a></li> <li><a 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class="mw-portlet mw-portlet-dock-bottom emptyPortlet" id="p-dock-bottom"> <ul> </ul> </div> <script>(RLQ=window.RLQ||[]).push(function(){mw.config.set({"wgHostname":"mw-web.codfw.main-5fc656d596-79nnc","wgBackendResponseTime":210,"wgPageParseReport":{"limitreport":{"cputime":"1.221","walltime":"1.497","ppvisitednodes":{"value":11114,"limit":1000000},"postexpandincludesize":{"value":318164,"limit":2097152},"templateargumentsize":{"value":18597,"limit":2097152},"expansiondepth":{"value":15,"limit":100},"expensivefunctioncount":{"value":9,"limit":500},"unstrip-depth":{"value":1,"limit":20},"unstrip-size":{"value":163775,"limit":5000000},"entityaccesscount":{"value":1,"limit":400},"timingprofile":["100.00% 1226.655 1 -total"," 25.39% 311.502 2 Template:Reflist"," 13.13% 161.087 10 Template:Navbox"," 12.96% 159.011 55 Template:SubatomicParticle"," 8.97% 110.081 1 Template:Particles"," 8.56% 104.970 3 Template:Lang"," 6.54% 80.250 14 Template:Cite_journal"," 6.54% 80.235 1 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