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class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Aniquilaci%C3%B3_electr%C3%B3-positr%C3%B3" title="Aniquilació electró-positró – Catalan" lang="ca" hreflang="ca" data-title="Aniquilació electró-positró" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/Elektron-positron_annihilation" title="Elektron-positron annihilation – Danish" lang="da" hreflang="da" data-title="Elektron-positron annihilation" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target"><span>Dansk</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Aniquilaci%C3%B3n_electr%C3%B3n-positr%C3%B3n" title="Aniquilación electrón-positrón – Spanish" lang="es" hreflang="es" data-title="Aniquilación electrón-positrón" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D9%86%D8%A7%D8%A8%D9%88%D8%AF%DB%8C_%D8%A7%D9%84%DA%A9%D8%AA%D8%B1%D9%88%D9%86-%D9%BE%D9%88%D8%B2%DB%8C%D8%AA%D8%B1%D9%88%D9%86" title="نابودی الکترون-پوزیترون – Persian" lang="fa" hreflang="fa" data-title="نابودی الکترون-پوزیترون" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Annihilation_%C3%A9lectron-positron" title="Annihilation électron-positron – French" lang="fr" hreflang="fr" data-title="Annihilation électron-positron" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EC%A0%84%EC%9E%90-%EC%96%91%EC%A0%84%EC%9E%90_%EC%8C%8D%EC%86%8C%EB%A9%B8" title="전자-양전자 쌍소멸 – Korean" lang="ko" hreflang="ko" data-title="전자-양전자 쌍소멸" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Annichilazione_elettrone-positrone" title="Annichilazione elettrone-positrone – Italian" lang="it" hreflang="it" data-title="Annichilazione elettrone-positrone" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-he mw-list-item"><a href="https://he.wikipedia.org/wiki/%D7%90%D7%99%D7%95%D7%9F_%D7%A9%D7%9C_%D7%90%D7%9C%D7%A7%D7%98%D7%A8%D7%95%D7%9F_%D7%95%D7%A4%D7%95%D7%96%D7%99%D7%98%D7%A8%D7%95%D7%9F" title="איון של אלקטרון ופוזיטרון – Hebrew" lang="he" hreflang="he" data-title="איון של אלקטרון ופוזיטרון" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target"><span>עברית</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Positronannihilatie" title="Positronannihilatie – Dutch" lang="nl" hreflang="nl" data-title="Positronannihilatie" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-pa mw-list-item"><a href="https://pa.wikipedia.org/wiki/%E0%A8%87%E0%A8%B2%E0%A9%88%E0%A8%95%E0%A8%9F%E0%A9%8D%E0%A8%B0%E0%A9%8B%E0%A8%A8-%E0%A8%AA%E0%A9%8B%E0%A8%9C%E0%A8%BC%E0%A9%80%E0%A8%9F%E0%A8%B0%E0%A9%8B%E0%A8%A8_%E0%A8%B5%E0%A8%BF%E0%A8%A8%E0%A8%BE%E0%A8%B8%E0%A8%BC" title="ਇਲੈਕਟ੍ਰੋਨ-ਪੋਜ਼ੀਟਰੋਨ ਵਿਨਾਸ਼ – Punjabi" lang="pa" hreflang="pa" data-title="ਇਲੈਕਟ੍ਰੋਨ-ਪੋਜ਼ੀਟਰੋਨ ਵਿਨਾਸ਼" data-language-autonym="ਪੰਜਾਬੀ" data-language-local-name="Punjabi" class="interlanguage-link-target"><span>ਪੰਜਾਬੀ</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Aniquila%C3%A7%C3%A3o_p%C3%B3sitron-el%C3%A9tron" title="Aniquilação pósitron-elétron – Portuguese" lang="pt" hreflang="pt" data-title="Aniquilação pósitron-elétron" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-sl mw-list-item"><a href="https://sl.wikipedia.org/wiki/Anihilacija_para" title="Anihilacija para – Slovenian" lang="sl" hreflang="sl" data-title="Anihilacija para" data-language-autonym="Slovenščina" data-language-local-name="Slovenian" class="interlanguage-link-target"><span>Slovenščina</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/Parintuho" title="Parintuho – Finnish" lang="fi" hreflang="fi" data-title="Parintuho" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-th mw-list-item"><a href="https://th.wikipedia.org/wiki/%E0%B8%9B%E0%B8%A3%E0%B8%B0%E0%B8%A5%E0%B8%B1%E0%B8%A2%E0%B8%AD%E0%B8%B4%E0%B9%80%E0%B8%A5%E0%B9%87%E0%B8%81%E0%B8%95%E0%B8%A3%E0%B8%AD%E0%B8%99%E2%80%93%E0%B9%82%E0%B8%9E%E0%B8%8B%E0%B8%B4%E0%B8%95%E0%B8%A3%E0%B8%AD%E0%B8%99" title="ประลัยอิเล็กตรอน–โพซิตรอน – Thai" lang="th" hreflang="th" 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href="/wiki/File:Annihilation.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/b/b2/Annihilation.png/330px-Annihilation.png" decoding="async" width="330" height="163" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/b2/Annihilation.png/495px-Annihilation.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/b2/Annihilation.png/660px-Annihilation.png 2x" data-file-width="2266" data-file-height="1116" /></a><figcaption>Naturally occurring electron-positron annihilation as a result of beta plus decay</figcaption></figure> <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 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.mw-parser-output .sidebar:not(.notheme) .sidebar-title-with-pretitle{background:transparent!important}html.skin-theme-clientpref-os .mw-parser-output .sidebar:not(.notheme) .sidebar-title-with-pretitle a{color:var(--color-progressive)!important}}@media print{body.ns-0 .mw-parser-output .sidebar{display:none!important}}</style><table class="sidebar sidebar-collapse nomobile nowraplinks"><tbody><tr><th class="sidebar-title"><a href="/wiki/Antimatter" title="Antimatter">Antimatter</a></th></tr><tr><td class="sidebar-image"><span class="skin-invert-image" typeof="mw:File"><a href="/wiki/File:ElectronPositronAnnihilation.svg" class="mw-file-description" title="A Feynman diagram showing the annihilation of an electron and a positron (antielectron), creating a photon that later decays into an new electron–positron pair."><img alt="A Feynman diagram showing the annihilation of an electron and a positron (antielectron), creating a photon that later decays into an new electron–positron pair." src="//upload.wikimedia.org/wikipedia/commons/thumb/0/0a/ElectronPositronAnnihilation.svg/150px-ElectronPositronAnnihilation.svg.png" decoding="async" width="150" height="88" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/0/0a/ElectronPositronAnnihilation.svg/225px-ElectronPositronAnnihilation.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/0/0a/ElectronPositronAnnihilation.svg/300px-ElectronPositronAnnihilation.svg.png 2x" data-file-width="808" data-file-height="475" /></a></span></td></tr><tr><td class="sidebar-content" style="padding-bottom:2px"> <div class="sidebar-list mw-collapsible mw-collapsed"><div class="sidebar-list-title" style="padding-left:2px; background:lavender;color: var(--color-base)"><a href="/wiki/Antiparticle" title="Antiparticle">Antiparticles</a></div><div class="sidebar-list-content mw-collapsible-content hlist"> <ul><li><a href="/wiki/Positron" title="Positron">Positron</a></li> <li><a href="/wiki/Antiproton" title="Antiproton">Antiproton</a></li> <li><a href="/wiki/Antineutron" title="Antineutron">Antineutron</a></li> <li><a href="/wiki/Antihydrogen" title="Antihydrogen">Antihydrogen</a></li> <li><a href="/wiki/Antihelium" class="mw-redirect" title="Antihelium">Antihelium</a></li></ul> <p><b><a href="/wiki/Onium" title="Onium">Onia</a></b> </p> <ul><li><a href="/wiki/Antiprotonic_hydrogen" class="mw-redirect" title="Antiprotonic hydrogen">Antiprotonic hydrogen</a></li> <li><a href="/wiki/Antiprotonic_helium" title="Antiprotonic helium">Antiprotonic helium</a></li> <li><a href="/wiki/Muonium" title="Muonium">Muonium</a></li> <li><a href="/wiki/True_muonium" title="True muonium">True muonium</a></li> <li><a href="/wiki/Pionium" title="Pionium">Pionium</a></li> <li><a href="/wiki/Positronium" title="Positronium">Positronium</a></li> <li><a href="/wiki/Quarkonium" title="Quarkonium">Quarkonium</a></li></ul></div></div></td> </tr><tr><td class="sidebar-content" style="padding-bottom:2px"> <div class="sidebar-list mw-collapsible mw-collapsed"><div class="sidebar-list-title" style="padding-left:2px; background:lavender;color: var(--color-base)">Concepts and phenomena</div><div class="sidebar-list-content mw-collapsible-content hlist"> <ul><li><a href="/wiki/Annihilation" title="Annihilation">Annihilation</a></li> <li><a href="/wiki/Baryogenesis" title="Baryogenesis">Baryogenesis</a></li> <li><a href="/wiki/Baryon_asymmetry" title="Baryon asymmetry">Baryon asymmetry</a></li> <li><a href="/wiki/Antimatter_comet" title="Antimatter comet">Comet</a></li> <li><a href="/wiki/CP_violation" title="CP violation">CP violation</a></li> <li><a href="/wiki/Gravitational_interaction_of_antimatter" title="Gravitational interaction of antimatter">Gravitational interaction</a></li> <li><a href="/wiki/Positron_emission" title="Positron emission">Positron emission</a></li></ul></div></div></td> </tr><tr><td class="sidebar-content" style="padding-bottom:2px"> <div class="sidebar-list mw-collapsible mw-collapsed"><div class="sidebar-list-title" style="padding-left:2px; background:lavender;color: var(--color-base)">Devices</div><div class="sidebar-list-content mw-collapsible-content hlist"> <ul><li><a href="/wiki/Cloud_chamber" title="Cloud chamber">Cloud chamber</a></li> <li><a href="/wiki/Particle_accelerator" title="Particle accelerator">Particle accelerator</a> <ul><li><a href="/wiki/Antiproton_decelerator" class="mw-redirect" title="Antiproton decelerator">Antiproton decelerator</a></li> <li><a href="/wiki/Relativistic_Heavy_Ion_Collider" title="Relativistic Heavy Ion Collider">Relativistic Heavy Ion Collider</a></li></ul></li> <li><a href="/wiki/Penning_trap" title="Penning trap">Penning trap</a></li></ul></div></div></td> </tr><tr><td class="sidebar-content" style="padding-bottom:2px"> <div class="sidebar-list mw-collapsible mw-collapsed"><div class="sidebar-list-title" style="padding-left:2px; background:lavender;color: var(--color-base)">Uses</div><div class="sidebar-list-content mw-collapsible-content hlist"> <ul><li><a href="/wiki/Positron_emission_tomography" title="Positron emission tomography">Positron emission tomography</a></li> <li><a href="/wiki/Antimatter#Fuel" title="Antimatter">Fuel</a></li> <li><a href="/wiki/Antimatter_weapon" title="Antimatter weapon">Weapon</a></li></ul></div></div></td> </tr><tr><td class="sidebar-content" style="padding-bottom:2px"> <div class="sidebar-list mw-collapsible mw-collapsed"><div class="sidebar-list-title" style="padding-left:2px; background:lavender;color: var(--color-base)">Scientists</div><div class="sidebar-list-content mw-collapsible-content hlist"> <ul><li><a href="/wiki/Carl_David_Anderson" title="Carl David Anderson">Carl David Anderson</a></li> <li><a href="/wiki/Paul_Dirac" title="Paul Dirac">Paul Dirac</a></li> <li><a href="/wiki/Andrei_Sakharov" title="Andrei Sakharov">Andrei Sakharov</a></li> <li><a href="/wiki/CERN" title="CERN">CERN</a></li></ul></div></div></td> </tr><tr><td class="sidebar-navbar" style="padding:0 2px"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><style data-mw-deduplicate="TemplateStyles:r1239400231">.mw-parser-output .navbar{display:inline;font-size:88%;font-weight:normal}.mw-parser-output .navbar-collapse{float:left;text-align:left}.mw-parser-output .navbar-boxtext{word-spacing:0}.mw-parser-output .navbar ul{display:inline-block;white-space:nowrap;line-height:inherit}.mw-parser-output .navbar-brackets::before{margin-right:-0.125em;content:"[ "}.mw-parser-output .navbar-brackets::after{margin-left:-0.125em;content:" ]"}.mw-parser-output .navbar li{word-spacing:-0.125em}.mw-parser-output .navbar a>span,.mw-parser-output .navbar a>abbr{text-decoration:inherit}.mw-parser-output .navbar-mini abbr{font-variant:small-caps;border-bottom:none;text-decoration:none;cursor:inherit}.mw-parser-output .navbar-ct-full{font-size:114%;margin:0 7em}.mw-parser-output .navbar-ct-mini{font-size:114%;margin:0 4em}html.skin-theme-clientpref-night .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}}@media print{.mw-parser-output .navbar{display:none!important}}</style><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Antimatter" title="Template:Antimatter"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Antimatter" title="Template talk:Antimatter"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Antimatter" title="Special:EditPage/Template:Antimatter"><abbr title="Edit this template">e</abbr></a></li></ul></div></td></tr></tbody></table> <p><b>Electron–positron annihilation</b> occurs when an <a href="/wiki/Electron" title="Electron">electron</a> (<span style="white-space:nowrap;"><span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1.0em;font-size:80%;text-align:right"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span>e<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1.0em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">−</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span></span>) and a <a href="/wiki/Positron" title="Positron">positron</a> (<span style="white-space:nowrap;"><span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1.0em;font-size:80%;text-align:right"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span>e<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1.0em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">+</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span></span>, the electron's <a href="/wiki/Antiparticle" title="Antiparticle">antiparticle</a>) collide. At low energies, the result of the collision is the <a href="/wiki/Annihilation" title="Annihilation">annihilation</a> of the electron and positron, and the creation of energetic <a href="/wiki/Photon" title="Photon">photons</a>: </p> <dl><dd><span style="white-space:nowrap;"><span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1.0em;font-size:80%;text-align:right"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span>e<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1.0em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">−</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span></span> + <span style="white-space:nowrap;"><span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1.0em;font-size:80%;text-align:right"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span>e<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1.0em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">+</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span></span> → <span style="white-space:nowrap;"><span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1.0em;font-size:80%;text-align:right"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span>γ<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1.0em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span></span> + <span style="white-space:nowrap;"><span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1.0em;font-size:80%;text-align:right"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span>γ<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1.0em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span></span></dd></dl> <p>At high energies, other particles, such as <a href="/wiki/B_meson" title="B meson">B mesons</a> or the <a href="/wiki/W_and_Z_bosons" title="W and Z bosons">W and Z bosons</a>, can be created. All processes must satisfy a number of <a href="/wiki/Conservation_law_(physics)" class="mw-redirect" title="Conservation law (physics)">conservation laws</a>, including: </p> <ul><li><a href="/wiki/Charge_conservation" title="Charge conservation">Conservation of electric charge</a>. The net <a href="/wiki/Electric_charge" title="Electric charge">charge</a> before and after is zero.</li> <li>Conservation of <a href="/wiki/Momentum" title="Momentum">linear momentum</a> and total <a href="/wiki/Energy" title="Energy">energy</a>. This forbids the creation of a single photon. However, in <a href="/wiki/Quantum_field_theory" title="Quantum field theory">quantum field theory</a> this process is allowed; see <a href="/wiki/Annihilation#Examples" title="Annihilation">examples of annihilation</a>.</li> <li>Conservation of <a href="/wiki/Angular_momentum" title="Angular momentum">angular momentum</a>.</li> <li>Conservation of total (i.e. net) <a href="/wiki/Lepton_number" title="Lepton number">lepton number</a>, which is the number of leptons (such as the electron) minus the number of antileptons (such as the positron); this can be described as a <a href="/wiki/Matter#Conservation_of_matter" title="Matter">conservation of (net) matter</a> law.</li></ul> <p>As with any two charged objects, electrons and positrons may also interact with each other without annihilating, in general by <a href="/wiki/Elastic_scattering" title="Elastic scattering">elastic scattering</a>. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Low-energy_case">Low-energy case</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Electron%E2%80%93positron_annihilation&action=edit&section=1" title="Edit section: Low-energy case"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>There are only a very limited set of possibilities for the final state. The most probable is the creation of two or more gamma photons. Conservation of energy and linear momentum forbid the creation of only one photon. (An exception to this rule can occur for tightly bound atomic electrons.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>) In the most common case, two gamma photons are created, each with <a href="/wiki/Photon_energy" title="Photon energy">energy</a> equal to the <a href="/wiki/Rest_energy" class="mw-redirect" title="Rest energy">rest energy</a> of the electron or positron (<span class="nowrap"><span data-sort-value="6986818712184856999♠"></span>0.511 <a href="/wiki/Electronvolt" title="Electronvolt">MeV</a></span>).<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> A convenient <a href="/wiki/Frame_of_reference" title="Frame of reference">frame of reference</a> is that in which the system has <a href="/wiki/Center_of_mass_frame" class="mw-redirect" title="Center of mass frame">no net linear momentum</a> before the annihilation; thus, after collision, the gamma photons are emitted in opposite directions. It is also common for three to be created, since in some angular momentum states, this is necessary to conserve <a href="/wiki/C_parity" title="C parity">charge parity</a>.<sup id="cite_ref-griffiths_3-0" class="reference"><a href="#cite_note-griffiths-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> It is also possible to create any larger number of photons, but the probability becomes lower with each additional gamma photon because these more complex processes have lower <a href="/wiki/Probability_amplitude" title="Probability amplitude">probability amplitudes</a>. </p><p>Since <a href="/wiki/Neutrino" title="Neutrino">neutrinos</a> also have a smaller mass than electrons, it is also possible – but exceedingly unlikely – for the annihilation to produce one or more neutrino–<a href="/wiki/Antineutrino" class="mw-redirect" title="Antineutrino">antineutrino</a> pairs. The probability for such process is on the order of 10000 times less likely than the annihilation into photons. The same would be true for any other particles, which are as light, as long as they share at least one <a href="/wiki/Fundamental_interaction" title="Fundamental interaction">fundamental interaction</a> with electrons and no conservation laws forbid it. However, no other such particles are known. </p> <div class="mw-heading mw-heading2"><h2 id="High-energy_case">High-energy case</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Electron%E2%80%93positron_annihilation&action=edit&section=2" title="Edit section: High-energy case"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>If either the electron or positron, or both, have appreciable <a href="/wiki/Kinetic_energy" title="Kinetic energy">kinetic energies</a>, other heavier particles can also be produced (such as <a href="/wiki/D_meson" title="D meson">D mesons</a> or <a href="/wiki/B_meson" title="B meson">B mesons</a>), since there is enough kinetic energy in the relative velocities to provide the <a href="/wiki/Rest_energy" class="mw-redirect" title="Rest energy">rest energies</a> of those particles. Alternatively, it is possible to produce photons and other light particles, but they will emerge with higher kinetic energies. </p><p>At energies near and beyond the mass of the carriers of the <a href="/wiki/Weak_interaction" title="Weak interaction">weak force</a>, the <a href="/wiki/W_and_Z_bosons" title="W and Z bosons">W and Z bosons</a>, the strength of the weak force becomes comparable to the <a href="/wiki/Electromagnetism" title="Electromagnetism">electromagnetic</a> force.<sup id="cite_ref-griffiths_3-1" class="reference"><a href="#cite_note-griffiths-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> As a result, it becomes much easier to produce particles such as neutrinos that interact only weakly with other matter. </p><p>The heaviest particle pairs yet produced by electron–positron annihilation in <a href="/wiki/Particle_accelerator" title="Particle accelerator">particle accelerators</a> are <a href="/wiki/W_boson" class="mw-redirect" title="W boson"><span style="white-space:nowrap;"><span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1.0em;font-size:80%;text-align:right"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span>W<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1.0em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">+</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span></span>–<span style="white-space:nowrap;"><span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1.0em;font-size:80%;text-align:right"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span>W<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:0.8em;line-height:1.0em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline">−</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sub></span></span></span></a> pairs (mass 80.385 GeV/c<sup>2</sup> × 2). The heaviest single-charged particle is the <a href="/wiki/Z_boson" class="mw-redirect" title="Z boson">Z boson</a> (mass 91.188 GeV/c<sup>2</sup>). The driving motivation for constructing the <a href="/wiki/International_Linear_Collider" title="International Linear Collider">International Linear Collider</a> is to produce the <a href="/wiki/Higgs_boson" title="Higgs boson">Higgs bosons</a> (mass 125.09 GeV/c<sup>2</sup>) in this way.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (June 2020)">citation needed</span></a></i>]</sup> </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Electron_Positron_Annihilation.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Electron_Positron_Annihilation.png/220px-Electron_Positron_Annihilation.png" decoding="async" width="220" height="210" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Electron_Positron_Annihilation.png/330px-Electron_Positron_Annihilation.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Electron_Positron_Annihilation.png/440px-Electron_Positron_Annihilation.png 2x" data-file-width="788" data-file-height="753" /></a><figcaption>Electron/positron annihilation at various energies</figcaption></figure> <div class="mw-heading mw-heading2"><h2 id="Practical_uses">Practical uses</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Electron%E2%80%93positron_annihilation&action=edit&section=3" title="Edit section: Practical uses"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The electron–positron annihilation process is the physical phenomenon relied on as the basis of <a href="/wiki/Positron_emission_tomography" title="Positron emission tomography">positron emission tomography</a> (PET) and <a href="/wiki/Positron_annihilation_spectroscopy" title="Positron annihilation spectroscopy">positron annihilation spectroscopy</a> (PAS). It is also used as a method of measuring the <a href="/wiki/Fermi_surface" title="Fermi surface">Fermi surface</a> and <a href="/wiki/Band_structure" class="mw-redirect" title="Band structure">band structure</a> in <a href="/wiki/Metal" title="Metal">metals</a> by a technique called <a href="/wiki/Angular_Correlation_of_Electron_Positron_Annihilation_Radiation" title="Angular Correlation of Electron Positron Annihilation Radiation">Angular Correlation of Electron Positron Annihilation Radiation</a>. It is also used for nuclear transition. Positron annihilation spectroscopy is also used for the study of <a href="/wiki/Crystallographic_defect" title="Crystallographic defect">crystallographic defects</a> in metals and semiconductors; it is considered the only direct probe for vacancy-type defects.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Reverse_reaction">Reverse reaction</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Electron%E2%80%93positron_annihilation&action=edit&section=4" title="Edit section: Reverse reaction"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The reverse reaction, electron–positron creation, is a form of <a href="/wiki/Pair_production" title="Pair production">pair production</a> governed by <a href="/wiki/Two-photon_physics" title="Two-photon physics">two-photon physics</a>. </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Electron%E2%80%93positron_annihilation&action=edit&section=5" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Bhabha_scattering" title="Bhabha scattering">Bhabha scattering</a></li> <li><a href="/wiki/List_of_particles" title="List of particles">List of particles</a></li> <li><a href="/wiki/Meitner%E2%80%93Hupfeld_effect" title="Meitner–Hupfeld effect">Meitner–Hupfeld effect</a></li> <li><a href="/wiki/Pair_production" title="Pair production">Pair production</a></li> <li><a href="/wiki/Positronium" title="Positronium">Positronium</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Electron%E2%80%93positron_annihilation&action=edit&section=6" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></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"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text"> <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 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