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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">     <html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en" xmlns:og="http://ogp.me/ns#" xmlns:fb="http://ogp.me/ns/fb#"> <head> <title>Measurement of the $K^+ \to \pi^+ \gamma \gamma$ decay - CERN Document Server</title> <link href='https://framework.web.cern.ch/framework/2.0/fonts/PTSansWeb/PTSansWeb.css' rel='stylesheet' type='text/css' /> <link rel="stylesheet" href="https://cds.cern.ch/img/invenio.css?v=20141127" type="text/css" /> <link rel="stylesheet" href="https://cds.cern.ch/img/cern_theme/css/cern_theme.css?v=20141127" type="text/css" /> <link rel="stylesheet"href="/css/font-awesome.min.css"> <meta http-equiv="X-UA-Compatible" content="IE=Edge"/> <link rel="stylesheet" href="https://cds.cern.ch/img/cern_toolbar/css/toolbar.css" type="text/css" />    <link rel="canonical" href="https://cds.cern.ch/record/2869421" /> <link rel="alternate" hreflang="el" href="https://cds.cern.ch/record/2869421?ln=el" /> <link rel="alternate" hreflang="fr" href="https://cds.cern.ch/record/2869421?ln=fr" /> <link rel="alternate" hreflang="bg" href="https://cds.cern.ch/record/2869421?ln=bg" /> <link rel="alternate" hreflang="zh-TW" href="https://cds.cern.ch/record/2869421?ln=zh_TW" /> <link rel="alternate" hreflang="pt" href="https://cds.cern.ch/record/2869421?ln=pt" /> <link rel="alternate" hreflang="no" href="https://cds.cern.ch/record/2869421?ln=no" /> <link rel="alternate" hreflang="hr" href="https://cds.cern.ch/record/2869421?ln=hr" /> <link rel="alternate" hreflang="ca" href="https://cds.cern.ch/record/2869421?ln=ca" /> <link rel="alternate" hreflang="de" href="https://cds.cern.ch/record/2869421?ln=de" /> <link rel="alternate" hreflang="it" href="https://cds.cern.ch/record/2869421?ln=it" /> <link rel="alternate" hreflang="zh-CN" href="https://cds.cern.ch/record/2869421?ln=zh_CN" /> <link rel="alternate" hreflang="sv" href="https://cds.cern.ch/record/2869421?ln=sv" /> <link rel="alternate" hreflang="sk" href="https://cds.cern.ch/record/2869421?ln=sk" /> <link rel="alternate" hreflang="en" href="https://cds.cern.ch/record/2869421?ln=en" /> <link rel="alternate" hreflang="pl" href="https://cds.cern.ch/record/2869421?ln=pl" /> <link rel="alternate" hreflang="ru" href="https://cds.cern.ch/record/2869421?ln=ru" /> <link rel="alternate" hreflang="ka" href="https://cds.cern.ch/record/2869421?ln=ka" /> <link rel="alternate" hreflang="ja" href="https://cds.cern.ch/record/2869421?ln=ja" /> <link rel="alternate" hreflang="es" href="https://cds.cern.ch/record/2869421?ln=es" /> <link rel="alternate" type="application/rss+xml" title="CERN Document Server RSS" href="/rss?ln=en" /> <link rel="search" type="application/opensearchdescription+xml" href="https://cds.cern.ch/opensearchdescription" title="CERN Document Server" /> <link rel="unapi-server" type="application/xml" title="unAPI" href="https://cds.cern.ch/unapi" /> <link rel="apple-touch-icon" href="/apple-touch-icon.png"/> <link rel="apple-touch-icon-precomposed" href="/apple-touch-icon-precomposed.png"/> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta http-equiv="Content-Language" content="en" /> <meta name="description" content="A sample of 3984 candidates of the $K^+ \to \pi^+ \gamma \gamma$ decay, with an estimated background of $291 \pm 14$ events, was collected by the NA62 experiment at CERN during 2017–2018. In order to describe the observed di-photon mass spectrum, the next-to-leading order contribution in chiral perturbation theory was found to be necessary. The decay branching ratio in the full kinematic range is measured to be ($9.61 \pm 0.17) \times 10^{−7}$. The first search for production and prompt decay of an axion-like particle with gluon coupling in the process $K^+ \to \pi^+ a, a \to \gamma \gamma$ is also reported. A sample of 3984 candidates of the <math altimg="si1.svg"><msup><mrow><mi>K</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mi>π</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><mi>γ</mi><mi>γ</mi></math> decay, with an estimated background of <math altimg="si2.svg"><mn>291</mn><mo>±</mo><mn>14</mn></math> events, was collected by the NA62 experiment at CERN during 2017–2018. In order to describe the observed di-photon mass spectrum, the next-to-leading order contribution in chiral perturbation theory was found to be necessary. The decay branching ratio in the full kinematic range is measured to be <math altimg="si3.svg"><mo stretchy="false">(</mo><mn>9.61</mn><mo>±</mo><mn>0.17</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">−</mo><mn>7</mn></mrow></msup></math>. The first search for production and prompt decay of an axion-like particle with gluon coupling in the process <math altimg="si4.svg"><msup><mrow><mi>K</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mi>π</mi></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">+</mo></mrow></msup><mi>a</mi></math>, <math altimg="si5.svg"><mi>a</mi><mo stretchy="false">→</mo><mi>γ</mi><mi>γ</mi></math> is also reported. A sample of 3984 candidates of the $K^+\to\pi^+\gamma\gamma$ decay, with an estimated background of $291\pm14$ events, was collected by the NA62 experiment at CERN during 2017-2018. In order to describe the observed di-photon mass spectrum, the next-to-leading order contribution in chiral perturbation theory was found to be necessary. The decay branching ratio in the full kinematic range is measured to be $(9.61\pm0.17)\times10^{-7}$. The first search for production and prompt decay of an axion-like particle with gluon coupling in the process $K^+\to\pi^+a$, $a\to\gamma\gamma$ is also reported. Cortina Gil, Eduardo; Minucci, Elisa; Padolski, Sergey; Petrov, Plamen; Velghe, Bob; Bryman, Douglas; Fu, Ji; Numao, Toshio; Petrov, Yevgeniy; Wong, Vincent Wai Sum; Husek, Tomas; Kampf, Karol; Zamkovsky, Michal; Jerhot, Jan; Aliberti, Riccardo; Khoriauli, Gia; Kunze, Jonas; Lomidze, David; Marchevski, Radoslav; Peruzzo, Letizia; Vormstein, Mario; Wanke, Rainer; Cotta Ramusino, Angelo; Dalpiaz, Pietro; Fiorini, Massimiliano; Gamberini, Enrico; Gianoli, Alberto; Neri, Ilaria; Norton, Alan; Petrucci, Ferruccio; Wahl, Heinrich; Bizzeti, Andrea; Bucci, Francesca; Iacopini, Enrico; Latino, Giuseppe; Lenti, Massimo; Parenti, Andrea; Volpe, Roberta; Antonelli, Antonella; Gonnella, Francesco; Lamanna, Gianluca; Lanfranchi, Gaia; Tinti, Gemma; Martellotti, Silvia; Moulson, Matthew; Kozhuharov, Venelin; Litov, Leandar; Georgiev, Georgi; Raggi, Mauro; Spadaro, Tommaso; Ambrosino, Fabio; Fiorenza, Renato; Capussela, Tiziana; Corvino, Michele; Di Filippo, Domenico; Massarotti, Paolo; Mirra, Marco; 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<meta content="Rubin, Philip David" name="citation_author" /> <meta content="Menichetti, Ezio" name="citation_author" /> <meta content="10.1016/j.physletb.2024.138513" name="citation_doi" /> <meta content="Phys. Lett. B" name="citation_journal_title" /> <meta content="850" name="citation_volume" /> <meta content="138513" name="citation_firstpage" /> <meta content="2023/11/01" name="citation_publication_date" /> <meta name="citation_online_date" content="2023/09/05"> <meta content="arXiv:2311.01837" name="citation_technical_report_number" /> <meta content="CERN-EP-2023-247" name="citation_technical_report_number" /> <meta content="CERN-EP-DRAFT-NA62-2023-003" name="citation_technical_report_institution" /> <meta content="10.1016/j.physletb.2024.138513" name="citation_doi" /> <meta name="citation_pdf_url" content="https://cds.cern.ch/record/2869421/files/CERN-EP-2023-247.pdf" /> <meta name="citation_pdf_url" content="https://cds.cern.ch/record/2869421/files/2311.01837.pdf" /> <meta name="citation_pdf_url" content="https://cds.cern.ch/record/2869421/files/Publication.pdf" />  <meta content="Elsevier B.V." property="og:title" /> <meta content="Measurement of the K+ → π+γγ decay" property="og:title" /> <meta content="Measurement of the $K^+ \to \pi^+ \gamma \gamma$ decay" property="og:title" /> <meta content="website" property="og:type" /> <meta content="website" property="og:type" /> <meta content="https://cds.cern.ch/record/2869421" property="og:url" /> <meta name="twitter:image" content="https://cds.cern.ch/record/2869421/files/best_fit_c6.png" /> <meta property="og:image" content="https://cds.cern.ch/record/2869421/files/best_fit_c6.png" /> <meta property="og:image:secure_url" content="https://cds.cern.ch/record/2869421/files/best_fit_c6.png" /> <meta property="og:image" content="https://cds.cern.ch/record/2869421/files/dp_dm_data_colz_z02.png" /> <meta property="og:image:secure_url" content="https://cds.cern.ch/record/2869421/files/dp_dm_data_colz_z02.png" /> <meta property="og:image" content="https://cds.cern.ch/record/2869421/files/K2pi_mass_plot.png" /> <meta property="og:image:secure_url" content="https://cds.cern.ch/record/2869421/files/K2pi_mass_plot.png" /> <meta property="og:image" content="https://cds.cern.ch/record/2869421/files/best_fit_c4.png" /> <meta property="og:image:secure_url" content="https://cds.cern.ch/record/2869421/files/best_fit_c4.png" /> <meta property="og:image" content="https://cds.cern.ch/record/2869421/files/Kpigg_mass_plot.png" /> <meta property="og:image:secure_url" content="https://cds.cern.ch/record/2869421/files/Kpigg_mass_plot.png" /> <meta property="og:image" content="https://cds.cern.ch/record/2869421/files/UL_branching.png" /> <meta property="og:image:secure_url" content="https://cds.cern.ch/record/2869421/files/UL_branching.png" /> <meta property="og:image" content="https://cds.cern.ch/record/2869421/files/comparison_c6.png" /> <meta property="og:image:secure_url" content="https://cds.cern.ch/record/2869421/files/comparison_c6.png" /> <meta property="og:image" content="https://cds.cern.ch/record/2869421/files/NA62_BC11.png" /> <meta property="og:image:secure_url" content="https://cds.cern.ch/record/2869421/files/NA62_BC11.png" /> <meta property="og:image" content="https://cds.cern.ch/record/2869421/files/comparison_br.png" /> <meta property="og:image:secure_url" content="https://cds.cern.ch/record/2869421/files/comparison_br.png" /> <meta property="og:image" content="https://cds.cern.ch/record/2869421/files/number_of_signal_events.png" /> <meta property="og:image:secure_url" content="https://cds.cern.ch/record/2869421/files/number_of_signal_events.png" /> <meta property="og:image" content="https://cds.cern.ch/record/2869421/files/mi_vs_chpt.png" /> <meta property="og:image:secure_url" content="https://cds.cern.ch/record/2869421/files/mi_vs_chpt.png" /> <meta property="og:image" content="https://cds.cern.ch/record/2869421/files/dp_dm_bkg_z02.png" /> <meta property="og:image:secure_url" content="https://cds.cern.ch/record/2869421/files/dp_dm_bkg_z02.png" /> <meta property="og:image" content="https://cds.cern.ch/record/2869421/files/na62-sketch2.png" /> <meta property="og:image:secure_url" content="https://cds.cern.ch/record/2869421/files/na62-sketch2.png" /> <meta property="og:image" content="https://cds.cern.ch/record/2869421/files/Kpi3g_selection_merged_good_mysizex_Mpi0_excluded_v332.png" /> <meta property="og:image:secure_url" content="https://cds.cern.ch/record/2869421/files/Kpi3g_selection_merged_good_mysizex_Mpi0_excluded_v332.png" /> <meta content="CERN Document Server" property="og:site_name" /> <meta content="A sample of 3984 candidates of the K+→π+γγ decay, with an estimated background of 291±14 events, was collected by the NA62 experiment at CERN during 2017–2018. In order to describe the observed di-photon mass spectrum, the next-to-leading order contribution in chiral perturbation theory was found to be necessary. The decay branching ratio in the full kinematic range is measured to be (9.61±0.17)×10−7. The first search for production and prompt decay of an axion-like particle with gluon coupling in the process K+→π+a, a→γγ is also reported." property="og:description" /> <meta content="Elsevier B.V." property="og:description" /> <meta content="arXiv" property="og:description" /> <meta content="A sample of 3984 candidates of the $K^+\to\pi^+\gamma\gamma$ decay, with an estimated background of $291\pm14$ events, was collected by the NA62 experiment at CERN during 2017-2018. In order to describe the observed di-photon mass spectrum, the next-to-leading order contribution in chiral perturbation theory was found to be necessary. The decay branching ratio in the full kinematic range is measured to be $(9.61\pm0.17)\times10^{-7}$. The first search for production and prompt decay of an axion-like particle with gluon coupling in the process $K^+\to\pi^+a$, $a\to\gamma\gamma$ is also reported." property="og:description" /> <meta content="A sample of 3984 candidates of the $K^+ \to \pi^+ \gamma \gamma$ decay, with an estimated background of $291 \pm 14$ events, was collected by the NA62 experiment at CERN during 2017–2018. In order to describe the observed di-photon mass spectrum, the next-to-leading order contribution in chiral perturbation theory was found to be necessary. The decay branching ratio in the full kinematic range is measured to be ($9.61 \pm 0.17) \times 10^{−7}$. The first search for production and prompt decay of an axion-like particle with gluon coupling in the process $K^+ \to \pi^+ a, a \to \gamma \gamma$ is also reported." property="og:description" />  <meta content="summary" name="twitter:card" /> <meta content="summary" name="twitter:card" /> <style></style> </head> <body class="NA6232Papers search" lang="en">  <div id="cern-toolbar"> <h1><a href="http://cern.ch" title="CERN">CERN <span>Accelerating science</span></a></h1> <ul> <li class="cern-accountlinks"><a class="cern-account" href="https://cds.cern.ch/youraccount/login?ln=en&referer=https%3A//cds.cern.ch/record/2869421%3Fln%3Den" title="Sign in to your CERN account">Sign in</a></li> <li><a class="cern-directory" href="http://cern.ch/directory" title="Search CERN resources and browse the directory">Directory</a></li> </ul> </div>   <div role="banner" class="clearfix" id="header"> <div class="header-inner inner"> <hgroup class="clearfix"> <h2 id="site-name"> <a rel="home" title="Home" href="/"><span>CERN Document Server</span></a> </h2> <h3 id="site-slogan">Access articles, reports and multimedia content in HEP</h3> </hgroup> <div role="navigation" id="main-navigation" class="cdsmenu"> <h2 class="element-invisible">Main menu</h2><ul class="links inline clearfix"> <li class="menu-386 first active-trail"><a class="active-trail" href="https://cds.cern.ch/?ln=en">Search</a></li> <li class="menu-444 "><a class="" title="" href="https://cds.cern.ch/submit?ln=en">Submit</a></li> <li class="menu-426 "><a class="" href="https://cds.cern.ch/help/?ln=en">Help</a></li> <li class="leaf hassubcdsmenu"> <a hreflang="en" class="header" href="https://cds.cern.ch/youraccount/display?ln=en">Personalize</a> <ul class="subsubcdsmenu"><li><a href="https://cds.cern.ch/youralerts/list?ln=en">Your alerts</a></li><li><a href="https://cds.cern.ch/yourbaskets/display?ln=en">Your baskets</a></li><li><a href="https://cds.cern.ch/yourcomments?ln=en">Your comments</a></li><li><a href="https://cds.cern.ch/youralerts/display?ln=en">Your searches</a></li></ul></li> </ul> </div> </div> </div>  <table class="navtrailbox"> <tr> <td class="navtrailboxbody"> <a href="/?ln=en" class="navtrail">Home</a> > <a href="/collection/CERN%20Experiments?ln=en" class="navtrail">CERN Experiments</a> > <a href="/collection/Fixed%20Target%20Experiments?ln=en" class="navtrail">SPS Experiments</a> > <a href="/collection/NA62?ln=en" class="navtrail">NA62</a> > <a href="/collection/NA62%20Papers?ln=en" class="navtrail">NA62 Papers</a> > Measurement of the $K^+ \to \pi^+ \gamma \gamma$ decay </td> </tr> </table> </div> <div class="pagebody"><div class="pagebodystripemiddle"> <div class="detailedrecordbox"> <div class="detailedrecordtabs"> <div> <ul class="detailedrecordtabs"><li class="on first"><a href="/record/2869421/?ln=en">Information </a></li><li class=""><a href="/record/2869421/comments?ln=en">Discussion (20) </a></li><li class=""><a href="/record/2869421/files?ln=en">Files </a></li></ul> <div id="tabsSpacer" style="clear:both;height:0px"> </div></div> </div> <div class="detailedrecordboxcontent"> <div class="top-left-folded"></div> <div class="top-right-folded"></div> <div class="inside">  <abbr class="unapi-id" title="2869421"></abbr>  <link href="/img/download_and_embed_buttons.css" rel="stylesheet" type="text/css" /> <style type="text/css">  .video_talk_wrapper{ max-width: 640px; min-height: 360px; } </style> <table class="formatRecordTableFullWidth"> <tr> <td class="formatRecordHeader" style="background-image: url('/img/journals.jpg');" colspan="2">  Article </td> </tr> <tr><td class="formatRecordLabel"> Report number </td><td style="padding-left:5px;"><a href="http://arxiv.org/abs/arXiv:2311.01837">arXiv:2311.01837</a> ; CERN-EP-2023-247</td></tr> <tr><td class="formatRecordLabel"> Title </td><td style="padding-left:5px;"><b>Measurement of the $K^+ \to \pi^+ \gamma \gamma$ decay</b></td></tr> <tr><td class="formatRecordLabel" style="vertical-align:top;">Related title</td><td style="padding-left:5px; ">Measurement of the K+ → π+γγ decay<br/></td></tr> <style> .video_control_container, #video_controlbutton { display: none; }#video_detailbox_download {display: none;}#video_detailbox_embed {display: none;}</style> <div class="video_control_container"> <div style="box-sizing: inherit;position: relative;min-height: 1em;margin: 1em 0;background: #f8f8f9;padding: 1em 1.5em;line-height: 1.4285em;transition: opacity .1s ease,color .1s ease,background .1s ease,box-shadow .1s ease,-webkit-box-shadow .1s ease;border-radius: .28571429rem;font-size: 1.1em;margin-top: 0;margin-bottom: 6px;background-color: #f8ffff;color: #276f86;box-shadow: 0 0 0 1px #a9d5de inset,0 0 0 0 transparent;"> <i class="fa fa-info"></i><span style="padding-left: 9px;">If you experience any problem watching the video, click the download button below</span> </div> <a id="video_controlbutton_download" rel="download_button" class="video_controlbutton" href="#">Download</a> <a id="video_controlbutton_embed" class="video_controlbutton" href="#">Embed</a> </div> <div id="video_detailbox_download" style="margin:10px"> </div> <div id="video_detailbox_embed" style="margin:10px"> </div> <tr><td class="formatRecordLabel"> <span style="white-space:nowrap;">Author(s)</span> </td><td style="padding-left:5px;"> <script type="text/javascript"> function toggle_authors_visibility(){ var more = document.getElementById('more'); var link = document.getElementById('link'); var extension = document.getElementById('extension'); if (more.style.display=='none'){ more.style.display = ''; extension.style.display = 'none'; link.innerHTML = "Hide" } else { more.style.display = 'none'; extension.style.display = ''; link.innerHTML = "Show all 234 authors" } link.style.color = "rgb(204,0,0);" } function set_up(){ var extension = document.getElementById('extension'); extension.innerHTML = "NA62 Collaboration "; toggle_authors_visibility(); } </script> <a name="show_hide" /><p id="more" style=""><a href="https://cds.cern.ch/search?f=author&p=Cortina%20Gil%2C%20Eduardo&ln=en">Cortina Gil, Eduardo</a> (Louvain U., CP3) ; <a href="https://cds.cern.ch/search?f=author&p=Minucci%2C%20Elisa&ln=en">Minucci, Elisa</a> (Louvain U., CP3 ; Syracuse U.) ; <a href="https://cds.cern.ch/search?f=author&p=Padolski%2C%20Sergey&ln=en">Padolski, Sergey</a> (Louvain U., CP3) ; <a href="https://cds.cern.ch/search?f=author&p=Petrov%2C%20Plamen&ln=en">Petrov, Plamen</a> (Louvain U., CP3) ; <a href="https://cds.cern.ch/search?f=author&p=Velghe%2C%20Bob&ln=en">Velghe, Bob</a> (TRIUMF) ; <a href="https://cds.cern.ch/search?f=author&p=Bryman%2C%20Douglas&ln=en">Bryman, Douglas</a> (British Columbia U. ; TRIUMF) ; <a href="https://cds.cern.ch/search?f=author&p=Fu%2C%20Ji&ln=en">Fu, Ji</a> (British Columbia U.) ; <a href="https://cds.cern.ch/search?f=author&p=Numao%2C%20Toshio&ln=en">Numao, Toshio</a> (TRIUMF) ; <a href="https://cds.cern.ch/search?f=author&p=Petrov%2C%20Yevgeniy&ln=en">Petrov, Yevgeniy</a> (TRIUMF) ; <a href="https://cds.cern.ch/search?f=author&p=Wong%2C%20Vincent%20Wai%20Sum&ln=en">Wong, Vincent Wai Sum</a> (TRIUMF) ; <a href="https://cds.cern.ch/search?f=author&p=Husek%2C%20Tomas&ln=en">Husek, Tomas</a> (Charles U. ; Birmingham U.) ; <a href="https://cds.cern.ch/search?f=author&p=Kampf%2C%20Karol&ln=en">Kampf, Karol</a> (Charles U.) ; <a href="https://cds.cern.ch/search?f=author&p=Zamkovsky%2C%20Michal&ln=en">Zamkovsky, Michal</a> (Charles U. ; CERN) ; <a href="https://cds.cern.ch/search?f=author&p=Jerhot%2C%20Jan&ln=en">Jerhot, Jan</a> (Charles U. ; Munich, Max Planck Inst.) ; <a href="https://cds.cern.ch/search?f=author&p=Aliberti%2C%20Riccardo&ln=en">Aliberti, Riccardo</a> (Mainz U., Inst. Phys. ; Helmholtz Inst., Mainz) ; <a href="https://cds.cern.ch/search?f=author&p=Khoriauli%2C%20Gia&ln=en">Khoriauli, Gia</a> (Mainz U., Inst. Phys. ; Wurzburg U.) ; <a href="https://cds.cern.ch/search?f=author&p=Kunze%2C%20Jonas&ln=en">Kunze, Jonas</a> (Mainz U., Inst. Phys.) ; <a href="https://cds.cern.ch/search?f=author&p=Lomidze%2C%20David&ln=en">Lomidze, David</a> (Mainz U., Inst. Phys. ; European XFEL, Hamburg) ; <a href="https://cds.cern.ch/search?f=author&p=Marchevski%2C%20Radoslav&ln=en">Marchevski, Radoslav</a> (CERN ; EPFL) ; <a href="https://cds.cern.ch/search?f=author&p=Peruzzo%2C%20Letizia&ln=en">Peruzzo, Letizia</a> (Mainz U., Inst. Phys.) ; <a href="https://cds.cern.ch/search?f=author&p=Vormstein%2C%20Mario&ln=en">Vormstein, Mario</a> (Mainz U., Inst. Phys.) ; <a href="https://cds.cern.ch/search?f=author&p=Wanke%2C%20Rainer&ln=en">Wanke, Rainer</a> (Mainz U., Inst. Phys.) ; <a href="https://cds.cern.ch/search?f=author&p=Cotta%20Ramusino%2C%20Angelo&ln=en">Cotta Ramusino, Angelo</a> (INFN, Ferrara) ; <a href="https://cds.cern.ch/search?f=author&p=Dalpiaz%2C%20Pietro&ln=en">Dalpiaz, Pietro</a> (Ferrara U.) ; <a href="https://cds.cern.ch/search?f=author&p=Fiorini%2C%20Massimiliano&ln=en">Fiorini, Massimiliano</a> (Ferrara U.) ; <a href="https://cds.cern.ch/search?f=author&p=Gamberini%2C%20Enrico&ln=en">Gamberini, Enrico</a> (CERN) ; <a href="https://cds.cern.ch/search?f=author&p=Gianoli%2C%20Alberto&ln=en">Gianoli, Alberto</a> (INFN, Ferrara) ; <a href="https://cds.cern.ch/search?f=author&p=Neri%2C%20Ilaria&ln=en">Neri, Ilaria</a> (Ferrara U.) ; <a href="https://cds.cern.ch/search?f=author&p=Norton%2C%20Alan&ln=en">Norton, Alan</a> (Ferrara U. ; Glasgow U.) ; <a href="https://cds.cern.ch/search?f=author&p=Petrucci%2C%20Ferruccio&ln=en">Petrucci, Ferruccio</a> (Ferrara U.) ; <a href="https://cds.cern.ch/search?f=author&p=Wahl%2C%20Heinrich&ln=en">Wahl, Heinrich</a> (Ferrara U. ; Mainz U., Inst. Phys.) ; <a href="https://cds.cern.ch/search?f=author&p=Bizzeti%2C%20Andrea&ln=en">Bizzeti, Andrea</a> (INFN, Florence ; Modena U.) ; <a href="https://cds.cern.ch/search?f=author&p=Bucci%2C%20Francesca&ln=en">Bucci, Francesca</a> (INFN, Florence) ; <a href="https://cds.cern.ch/search?f=author&p=Iacopini%2C%20Enrico&ln=en">Iacopini, Enrico</a> (Florence U.) ; <a href="https://cds.cern.ch/search?f=author&p=Latino%2C%20Giuseppe&ln=en">Latino, Giuseppe</a> (Florence U.) ; <a href="https://cds.cern.ch/search?f=author&p=Lenti%2C%20Massimo&ln=en">Lenti, Massimo</a> (Florence U.) ; <a href="https://cds.cern.ch/search?f=author&p=Parenti%2C%20Andrea&ln=en">Parenti, Andrea</a> (Florence U.) ; <a href="https://cds.cern.ch/search?f=author&p=Volpe%2C%20Roberta&ln=en">Volpe, Roberta</a> (Louvain U., CP3 ; INFN, Perugia) ; <a href="https://cds.cern.ch/search?f=author&p=Antonelli%2C%20Antonella&ln=en">Antonelli, Antonella</a> (Frascati) ; <a href="https://cds.cern.ch/search?f=author&p=Gonnella%2C%20Francesco&ln=en">Gonnella, Francesco</a> (Birmingham U.) ; <a href="https://cds.cern.ch/search?f=author&p=Lamanna%2C%20Gianluca&ln=en">Lamanna, Gianluca</a> (Pisa U.) ; <a href="https://cds.cern.ch/search?f=author&p=Lanfranchi%2C%20Gaia&ln=en">Lanfranchi, Gaia</a> (Frascati) ; <a href="https://cds.cern.ch/search?f=author&p=Tinti%2C%20Gemma&ln=en">Tinti, Gemma</a> (Frascati) ; <a href="https://cds.cern.ch/search?f=author&p=Martellotti%2C%20Silvia&ln=en">Martellotti, Silvia</a> (Frascati) ; <a href="https://cds.cern.ch/search?f=author&p=Moulson%2C%20Matthew&ln=en">Moulson, Matthew</a> (Frascati) ; <a href="https://cds.cern.ch/search?f=author&p=Kozhuharov%2C%20Venelin&ln=en">Kozhuharov, Venelin</a> (Frascati ; Sofiya U.) ; <a href="https://cds.cern.ch/search?f=author&p=Litov%2C%20Leandar&ln=en">Litov, Leandar</a> (Sofiya U.) ; <a href="https://cds.cern.ch/search?f=author&p=Georgiev%2C%20Georgi&ln=en">Georgiev, Georgi</a> (Frascati ; Sofiya U.) ; <a href="https://cds.cern.ch/search?f=author&p=Raggi%2C%20Mauro&ln=en">Raggi, Mauro</a> (Rome U.) ; <a href="https://cds.cern.ch/search?f=author&p=Spadaro%2C%20Tommaso&ln=en">Spadaro, Tommaso</a> (Frascati) ; <a href="https://cds.cern.ch/search?f=author&p=Ambrosino%2C%20Fabio&ln=en">Ambrosino, Fabio</a> (Naples U.) ; <a href="https://cds.cern.ch/search?f=author&p=Fiorenza%2C%20Renato&ln=en">Fiorenza, Renato</a> (Naples U. ; SSM, Naples) ; <a href="https://cds.cern.ch/search?f=author&p=Capussela%2C%20Tiziana&ln=en">Capussela, Tiziana</a> (Naples U.) ; <a href="https://cds.cern.ch/search?f=author&p=Corvino%2C%20Michele&ln=en">Corvino, Michele</a> (Naples U.) ; <a href="https://cds.cern.ch/search?f=author&p=Di%20Filippo%2C%20Domenico&ln=en">Di Filippo, Domenico</a> (Naples U.) ; <a href="https://cds.cern.ch/search?f=author&p=Massarotti%2C%20Paolo&ln=en">Massarotti, Paolo</a> (Naples U.) ; <a href="https://cds.cern.ch/search?f=author&p=Mirra%2C%20Marco&ln=en">Mirra, Marco</a> (Naples U.) ; <a href="https://cds.cern.ch/search?f=author&p=Napolitano%2C%20Marco&ln=en">Napolitano, Marco</a> (Naples U.) ; <a href="https://cds.cern.ch/search?f=author&p=Saracino%2C%20Giulio&ln=en">Saracino, Giulio</a> (Naples U.) ; <a href="https://cds.cern.ch/search?f=author&p=Anzivino%2C%20Giuseppina&ln=en">Anzivino, Giuseppina</a> (Perugia U.) ; <a href="https://cds.cern.ch/search?f=author&p=Imbergamo%2C%20Ermanno&ln=en">Imbergamo, Ermanno</a> (Perugia U.) ; <a href="https://cds.cern.ch/search?f=author&p=Lollini%2C%20Riccardo&ln=en">Lollini, Riccardo</a> (Perugia U.) ; <a href="https://cds.cern.ch/search?f=author&p=Santoni%2C%20Cristiano&ln=en">Santoni, Cristiano</a> (Perugia U.) ; <a href="https://cds.cern.ch/search?f=author&p=Brizioli%2C%20Francesco&ln=en">Brizioli, Francesco</a> (Perugia U. ; CERN) ; <a href="https://cds.cern.ch/search?f=author&p=Barbanera%2C%20Mattia&ln=en">Barbanera, Mattia</a> (INFN, Perugia) ; <a href="https://cds.cern.ch/search?f=author&p=Cenci%2C%20Patrizia&ln=en">Cenci, Patrizia</a> (INFN, Perugia) ; <a href="https://cds.cern.ch/search?f=author&p=Checcucci%2C%20Bruno&ln=en">Checcucci, Bruno</a> (INFN, Perugia) ; <a href="https://cds.cern.ch/search?f=author&p=Duk%2C%20Viacheslav&ln=en">Duk, Viacheslav</a> (Birmingham U. ; INFN, Perugia) ; <a href="https://cds.cern.ch/search?f=author&p=Lupi%2C%20Matteo&ln=en">Lupi, Matteo</a> (INFN, Perugia ; Goethe U., Frankfurt, Inst. 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<a href="https://cds.cern.ch/search?f=author&p=Lonardo%2C%20Alessandro&ln=en">Lonardo, Alessandro</a> (INFN, Rome) ; <a href="https://cds.cern.ch/search?f=author&p=Valente%2C%20Paolo&ln=en">Valente, Paolo</a> (INFN, Rome) ; <a href="https://cds.cern.ch/search?f=author&p=Vicini%2C%20Piero&ln=en">Vicini, Piero</a> (INFN, Rome) ; <a href="https://cds.cern.ch/search?f=author&p=Cretaro%2C%20Paolo&ln=en">Cretaro, Paolo</a> (INFN, Rome) ; <a href="https://cds.cern.ch/search?f=author&p=Turisini%2C%20Matteo&ln=en">Turisini, Matteo</a> (INFN, Rome) ; <a href="https://cds.cern.ch/search?f=author&p=Frezza%2C%20Ottorino&ln=en">Frezza, Ottorino</a> (INFN, Rome) ; <a href="https://cds.cern.ch/search?f=author&p=Ammendola%2C%20Roberto&ln=en">Ammendola, Roberto</a> (Rome U., Tor Vergata) ; <a href="https://cds.cern.ch/search?f=author&p=Bonaiuto%2C%20Vincenzo&ln=en">Bonaiuto, Vincenzo</a> (Rome U., Tor Vergata) ; <a href="https://cds.cern.ch/search?f=author&p=De%20Simone%2C%20Nicola&ln=en">De Simone, Nicola</a> (CERN ; DESY) ; <a href="https://cds.cern.ch/search?f=author&p=Federici%2C%20Luca&ln=en">Federici, Luca</a> (CERN) ; <a href="https://cds.cern.ch/search?f=author&p=Fucci%2C%20Adolfo&ln=en">Fucci, Adolfo</a> (Rome U., Tor Vergata) ; <a href="https://cds.cern.ch/search?f=author&p=Salamon%2C%20Andrea&ln=en">Salamon, Andrea</a> (Rome U., Tor Vergata) ; <a href="https://cds.cern.ch/search?f=author&p=Sargeni%2C%20Fausto&ln=en">Sargeni, Fausto</a> (Rome U., Tor Vergata) ; <a href="https://cds.cern.ch/search?f=author&p=Arcidiacono%2C%20Roberta&ln=en">Arcidiacono, Roberta</a> (Turin U. ; Piemonte Orientale U., Novara) ; <a href="https://cds.cern.ch/search?f=author&p=Biino%2C%20Cristina&ln=en">Biino, Cristina</a> (INFN, Turin) ; <a href="https://cds.cern.ch/search?f=author&p=Bloch-Devaux%2C%20Brigitte&ln=en">Bloch-Devaux, Brigitte</a> (Turin U.) ; <a href="https://cds.cern.ch/search?f=author&p=Boretto%2C%20Marco&ln=en">Boretto, Marco</a> (Turin U. ; CERN) ; <a href="https://cds.cern.ch/search?f=author&p=Filippi%2C%20Alessandra&ln=en">Filippi, Alessandra</a> (INFN, Turin) ; <a href="https://cds.cern.ch/search?f=author&p=Iacobuzio%2C%20Lorenza&ln=en">Iacobuzio, Lorenza</a> (Birmingham U.) ; <a href="https://cds.cern.ch/search?f=author&p=Marchetto%2C%20Flavio&ln=en">Marchetto, Flavio</a> (INFN, Turin) ; <a href="https://cds.cern.ch/search?f=author&p=Menichetti%2C%20Ezio&ln=en">Menichetti, Ezio</a> (Turin U.) ; <a href="https://cds.cern.ch/search?f=author&p=Migliore%2C%20Ernesto&ln=en">Migliore, Ernesto</a> (Turin U.) ; <a href="https://cds.cern.ch/search?f=author&p=Soldi%2C%20Dario&ln=en">Soldi, Dario</a> (Turin U.) ; <a href="https://cds.cern.ch/search?f=author&p=Engelfried%2C%20J%C3%BCrgen&ln=en">Engelfried, Jürgen</a> (San Luis Potosi U.) ; <a href="https://cds.cern.ch/search?f=author&p=Estrada-Tristan%2C%20Nora&ln=en">Estrada-Tristan, Nora</a> (San Luis Potosi U. ; Guanajuato U.) ; <a href="https://cds.cern.ch/search?f=author&p=Bragadireanu%2C%20Alexandru%20Mario&ln=en">Bragadireanu, Alexandru Mario</a> (Bucharest, IFIN-HH) ; <a href="https://cds.cern.ch/search?f=author&p=Ghinescu%2C%20Stefan%20Alexandru&ln=en">Ghinescu, Stefan Alexandru</a> (Bucharest, IFIN-HH) ; <a href="https://cds.cern.ch/search?f=author&p=Hutanu%2C%20Ovidiu%20Emanuel&ln=en">Hutanu, Ovidiu Emanuel</a> (Bucharest, IFIN-HH) ; <a href="https://cds.cern.ch/search?f=author&p=Enik%2C%20Temur&ln=en">Enik, Temur</a> ; <a href="https://cds.cern.ch/search?f=author&p=Falaleev%2C%20Valeri&ln=en">Falaleev, Valeri</a> (INFN, Perugia) ; <a href="https://cds.cern.ch/search?f=author&p=Kekelidze%2C%20Vladimir&ln=en">Kekelidze, Vladimir</a> ; <a href="https://cds.cern.ch/search?f=author&p=Korotkova%2C%20Anna&ln=en">Korotkova, Anna</a> ; <a href="https://cds.cern.ch/search?f=author&p=Madigozhin%2C%20Dmitry&ln=en">Madigozhin, Dmitry</a> ; <a href="https://cds.cern.ch/search?f=author&p=Misheva%2C%20Milena&ln=en">Misheva, Milena</a> (Sofiya, Inst. Nucl. Res.) ; <a href="https://cds.cern.ch/search?f=author&p=Molokanova%2C%20Natalia&ln=en">Molokanova, Natalia</a> ; <a href="https://cds.cern.ch/search?f=author&p=Movchan%2C%20Sergei&ln=en">Movchan, Sergei</a> ; <a href="https://cds.cern.ch/search?f=author&p=Polenkevich%2C%20Irina&ln=en">Polenkevich, Irina</a> ; <a href="https://cds.cern.ch/search?f=author&p=Potrebenikov%2C%20Yuri&ln=en">Potrebenikov, Yuri</a> ; <a href="https://cds.cern.ch/search?f=author&p=Shkarovskiy%2C%20Sergey&ln=en">Shkarovskiy, Sergey</a> ; <a href="https://cds.cern.ch/search?f=author&p=Zinchenko%2C%20Andrey&ln=en">Zinchenko, Andrey</a> ; <a href="https://cds.cern.ch/search?f=author&p=Baeva%2C%20Aigul&ln=en">Baeva, Aigul</a> ; <a href="https://cds.cern.ch/search?f=author&p=Baigarashev%2C%20Dosbol&ln=en">Baigarashev, Dosbol</a> (Eurasian Nat. U., Astana) ; <a href="https://cds.cern.ch/search?f=author&p=Emelyanov%2C%20Dmitry&ln=en">Emelyanov, Dmitry</a> ; <a href="https://cds.cern.ch/search?f=author&p=Fedotov%2C%20Sergei&ln=en">Fedotov, Sergei</a> ; <a href="https://cds.cern.ch/search?f=author&p=Khotyantsev%2C%20Alexey&ln=en">Khotyantsev, Alexey</a> ; <a href="https://cds.cern.ch/search?f=author&p=Gushchin%2C%20Evgeny&ln=en">Gushchin, Evgeny</a> ; <a href="https://cds.cern.ch/search?f=author&p=Kleimenova%2C%20Alina&ln=en">Kleimenova, Alina</a> (Louvain U., CP3 ; EPFL) ; <a href="https://cds.cern.ch/search?f=author&p=Kudenko%2C%20Yury&ln=en">Kudenko, Yury</a> ; <a href="https://cds.cern.ch/search?f=author&p=Kurochka%2C%20Viktoriia&ln=en">Kurochka, Viktoriia</a> ; <a href="https://cds.cern.ch/search?f=author&p=Medvedeva%2C%20Mariia&ln=en">Medvedeva, Mariia</a> ; <a href="https://cds.cern.ch/search?f=author&p=Mefodev%2C%20Aleksandr&ln=en">Mefodev, Aleksandr</a> ; <a href="https://cds.cern.ch/search?f=author&p=Shaikhiev%2C%20Artur&ln=en">Shaikhiev, Artur</a> (Louvain U., CP3 ; Lancaster U.) ; <a href="https://cds.cern.ch/search?f=author&p=Kholodenko%2C%20Sergey&ln=en">Kholodenko, Sergey</a> (INFN, Pisa) ; <a href="https://cds.cern.ch/search?f=author&p=Kurshetsov%2C%20Viktor&ln=en">Kurshetsov, Viktor</a> ; <a href="https://cds.cern.ch/search?f=author&p=Obraztsov%2C%20Vladimir&ln=en">Obraztsov, Vladimir</a> ; <a href="https://cds.cern.ch/search?f=author&p=Ostankov%2C%20Aleksandr&ln=en">Ostankov, Aleksandr</a> ; <a href="https://cds.cern.ch/search?f=author&p=Semenov%2C%20Vitali&ln=en">Semenov, Vitali</a> ; <a href="https://cds.cern.ch/search?f=author&p=Sugonyaev%2C%20Valentin&ln=en">Sugonyaev, Valentin</a> ; <a href="https://cds.cern.ch/search?f=author&p=Yushchenko%2C%20Oleg&ln=en">Yushchenko, Oleg</a> ; <a href="https://cds.cern.ch/search?f=author&p=Bician%2C%20Lubos&ln=en">Bician, Lubos</a> (Comenius U. ; Charles U.) ; <a href="https://cds.cern.ch/search?f=author&p=Blazek%2C%20Tomas&ln=en">Blazek, Tomas</a> (Comenius U.) ; <a href="https://cds.cern.ch/search?f=author&p=Cerny%2C%20Vladimir&ln=en">Cerny, Vladimir</a> (Comenius U.) ; <a href="https://cds.cern.ch/search?f=author&p=Koval%2C%20Michal&ln=en">Koval, Michal</a> (CERN ; Charles U.) ; <a href="https://cds.cern.ch/search?f=author&p=Kucerova%2C%20Zuzana&ln=en">Kucerova, Zuzana</a> (Comenius U. ; CERN) ; <a href="https://cds.cern.ch/search?f=author&p=Ceccucci%2C%20Augusto&ln=en">Ceccucci, Augusto</a> (CERN) ; <a href="https://cds.cern.ch/search?f=author&p=Bernhard%2C%20Johannes&ln=en">Bernhard, Johannes</a> (CERN) ; <a href="https://cds.cern.ch/search?f=author&p=Danielsson%2C%20Hans&ln=en">Danielsson, Hans</a> (CERN) ; <a href="https://cds.cern.ch/search?f=author&p=D%C3%B6brich%2C%20Babette&ln=en">Döbrich, Babette</a> (Munich, Max Planck Inst.) ; <a href="https://cds.cern.ch/search?f=author&p=Duval%2C%20Francois&ln=en">Duval, Francois</a> (CERN) ; <a href="https://cds.cern.ch/search?f=author&p=Gatignon%2C%20Lau&ln=en">Gatignon, Lau</a> (CERN ; Lancaster U.) ; <a href="https://cds.cern.ch/search?f=author&p=Guida%2C%20Roberto&ln=en">Guida, Roberto</a> (CERN) ; 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<a href="https://cds.cern.ch/search?f=author&p=Lazzeroni%2C%20Cristina&ln=en">Lazzeroni, Cristina</a> (Birmingham U.) ; <a href="https://cds.cern.ch/search?f=author&p=Fascianelli%2C%20Valeria&ln=en">Fascianelli, Valeria</a> (Birmingham U. ; Columbia U. (main)) ; <a href="https://cds.cern.ch/search?f=author&p=Lurkin%2C%20Nicolas&ln=en">Lurkin, Nicolas</a> (Birmingham U. ; Louvain U., CP3) ; <a href="https://cds.cern.ch/search?f=author&p=Newson%2C%20Francis&ln=en">Newson, Francis</a> (Birmingham U.) ; <a href="https://cds.cern.ch/search?f=author&p=Parkinson%2C%20Christopher&ln=en">Parkinson, Christopher</a> (Birmingham U.) ; <a href="https://cds.cern.ch/search?f=author&p=Romano%2C%20Angela&ln=en">Romano, Angela</a> (Birmingham U.) ; <a href="https://cds.cern.ch/search?f=author&p=Sergi%2C%20Antonino&ln=en">Sergi, Antonino</a> (Birmingham U. ; Genoa U.) ; <a href="https://cds.cern.ch/search?f=author&p=Sturgess%2C%20Andrew&ln=en">Sturgess, Andrew</a> (Birmingham U.) ; <a href="https://cds.cern.ch/search?f=author&p=Swallow%2C%20Joel&ln=en">Swallow, Joel</a> (Birmingham U. ; CERN) ; <a href="https://cds.cern.ch/search?f=author&p=Heath%2C%20Helen&ln=en">Heath, Helen</a> (Bristol U.) ; <a href="https://cds.cern.ch/search?f=author&p=Page%2C%20Ryan&ln=en">Page, Ryan</a> (Bristol U.) ; <a href="https://cds.cern.ch/search?f=author&p=Trilov%2C%20Stoyan&ln=en">Trilov, Stoyan</a> (Bristol U.) ; <a href="https://cds.cern.ch/search?f=author&p=Angelucci%2C%20Bruno&ln=en">Angelucci, Bruno</a> (Glasgow U.) ; <a href="https://cds.cern.ch/search?f=author&p=Britton%2C%20David&ln=en">Britton, David</a> (Glasgow U.) ; <a href="https://cds.cern.ch/search?f=author&p=Protopopescu%2C%20Dan&ln=en">Protopopescu, Dan</a> (Glasgow U.) ; <a href="https://cds.cern.ch/search?f=author&p=Graham%2C%20Connor&ln=en">Graham, Connor</a> (Glasgow U.) ; <a href="https://cds.cern.ch/search?f=author&p=Jones%2C%20Roger%20William%20Lewis&ln=en">Jones, Roger William Lewis</a> (Lancaster U.) ; <a href="https://cds.cern.ch/search?f=author&p=Dainton%2C%20John%20Bourke&ln=en">Dainton, John Bourke</a> (Lancaster U.) ; <a href="https://cds.cern.ch/search?f=author&p=Fry%2C%20John%20Richard&ln=en">Fry, John Richard</a> (Birmingham U.) ; <a href="https://cds.cern.ch/search?f=author&p=Fulton%2C%20Liam&ln=en">Fulton, Liam</a> (Liverpool U.) ; <a href="https://cds.cern.ch/search?f=author&p=Hutchcroft%2C%20David&ln=en">Hutchcroft, David</a> (Liverpool U.) ; <a href="https://cds.cern.ch/search?f=author&p=Carmignani%2C%20Joseph&ln=en">Carmignani, Joseph</a> (Lancaster U. ; Liverpool U.) ; <a href="https://cds.cern.ch/search?f=author&p=Massri%2C%20Karim&ln=en">Massri, Karim</a> (CERN) ; <a href="https://cds.cern.ch/search?f=author&p=Maurice%2C%20Emilie&ln=en">Maurice, Emilie</a> (Liverpool U. ; LLR, Palaiseau) ; <a href="https://cds.cern.ch/search?f=author&p=Wrona%2C%20Bozydar&ln=en">Wrona, Bozydar</a> (Liverpool U.) ; <a href="https://cds.cern.ch/search?f=author&p=Conovaloff%2C%20Adam&ln=en">Conovaloff, Adam</a> (George Mason U.) ; <a href="https://cds.cern.ch/search?f=author&p=Cooper%2C%20Peter&ln=en">Cooper, Peter</a> (George Mason U.) ; <a href="https://cds.cern.ch/search?f=author&p=Coward%2C%20David&ln=en">Coward, David</a> (George Mason U. ; SLAC) ; <a href="https://cds.cern.ch/search?f=author&p=Rubin%2C%20Philip%20David&ln=en">Rubin, Philip David</a> (George Mason U.) ; <a href="https://cds.cern.ch/search?f=author&p=Hives%2C%20Zdenko&ln=en">Hives, Zdenko</a> (Charles U.) ; <a href="https://cds.cern.ch/search?f=author&p=Akmete%2C%20Atakan%20Tugberk&ln=en">Akmete, Atakan Tugberk</a> (Mainz U., Inst. Phys.) ; <a href="https://cds.cern.ch/search?f=author&p=Soldani%2C%20Mattia&ln=en">Soldani, Mattia</a> (Ferrara U.) ; <a href="https://cds.cern.ch/search?f=author&p=Bandiera%2C%20Laura&ln=en">Bandiera, Laura</a> (INFN, Ferrara) ; <a href="https://cds.cern.ch/search?f=author&p=Mazzolari%2C%20Andrea&ln=en">Mazzolari, Andrea</a> (Ferrara U.) ; <a href="https://cds.cern.ch/search?f=author&p=Romagnoni%2C%20Marco&ln=en">Romagnoni, Marco</a> (INFN, Ferrara) ; <a href="https://cds.cern.ch/search?f=author&p=Sytov%2C%20Alexei&ln=en">Sytov, Alexei</a> (INFN, Ferrara) ; <a href="https://cds.cern.ch/search?f=author&p=Panichi%2C%20Ilaria&ln=en">Panichi, Ilaria</a> (Florence U.) ; <a href="https://cds.cern.ch/search?f=author&p=Lo%20Chiatto%2C%20Prisco&ln=en">Lo Chiatto, Prisco</a> (Florence U.) ; <a href="https://cds.cern.ch/search?f=author&p=D%27Errico%2C%20Mariaelena&ln=en">D'Errico, Mariaelena</a> (Naples U.) ; <a href="https://cds.cern.ch/search?f=author&p=Giordano%2C%20Raffaele&ln=en">Giordano, Raffaele</a> (Naples U.) ; <a href="https://cds.cern.ch/search?f=author&p=Briano%20Olvera%2C%20Alejandro&ln=en">Briano Olvera, Alejandro</a> (San Luis Potosi U.) ; <a href="https://cds.cern.ch/search?f=author&p=Reyes%20Santos%2C%20Marco%20Antonio&ln=en">Reyes Santos, Marco Antonio</a> (San Luis Potosi U. ; Guanajuato U.) ; <a href="https://cds.cern.ch/search?f=author&p=Boboc%2C%20Petre&ln=en">Boboc, Petre</a> (Bucharest, IFIN-HH) ; <a href="https://cds.cern.ch/search?f=author&p=Kereibay%2C%20Dias&ln=en">Kereibay, Dias</a> ; <a href="https://cds.cern.ch/search?f=author&p=Gorshanov%2C%20Konstantin&ln=en">Gorshanov, Konstantin</a> ; <a href="https://cds.cern.ch/search?f=author&p=Okhotnikov%2C%20Artem&ln=en">Okhotnikov, Artem</a> ; <a href="https://cds.cern.ch/search?f=author&p=Sadovskiy%2C%20Alexander&ln=en">Sadovskiy, Alexander</a> ; <a href="https://cds.cern.ch/search?f=author&p=Sanders%2C%20Jack&ln=en">Sanders, Jack</a> (Birmingham U.) ; <a href="https://cds.cern.ch/search?f=author&p=Kenworthy%2C%20Chandler&ln=en">Kenworthy, Chandler</a> (Birmingham U.) ; <a href="https://cds.cern.ch/search?f=author&p=De%20Martino%2C%20Bianca&ln=en">De Martino, Bianca</a> (Marseille, CPPM) ; <a href="https://cds.cern.ch/search?f=author&p=Rosa%2C%20Ilaria&ln=en">Rosa, Ilaria</a> (Naples U.) ; <a href="https://cds.cern.ch/search?f=author&p=Ceoletta%2C%20Marco&ln=en">Ceoletta, Marco</a> (CERN) ; <a href="https://cds.cern.ch/search?f=author&p=Rodriguez%20Rivera%2C%20Kevin%20Alexander&ln=en">Rodriguez Rivera, Kevin Alexander</a> (San Luis Potosi U.) ; <a href="https://cds.cern.ch/search?f=author&p=Lezki%2C%20Samet&ln=en">Lezki, Samet</a> (Munich, Max Planck Inst.)</p> <span id="extension"></span> <small><i><a id="link" href="#" onclick="toggle_authors_visibility()" style="color:rgb(204,0,0);"></a></i></small><script type="text/javascript">set_up()</script></td></tr> <tr><td class="formatRecordLabel"> Corporate <span style="white-space:nowrap;">author(s)</span> </td><td style="padding-left:5px;">The NA62 collaboration</td></tr> <tr><td class="formatRecordLabel"> Publication </td><td style="padding-left:5px;">2024-02-07</td></tr>  <script type="text/javascript"> /* * Changes the Imprint title to Date - Duration as requested by RQF0820114 * This is a hack not to touch the general imprint format element */ $(document).ready(function() { var collections = 'NA62_Papers ; ARTICLE'; if (collections.indexOf('E-LEARNING') > -1) { $('.cern-imprint-label').text('Date - Duration'); } }) </script> <tr><td class="formatRecordLabel cern-imprint-label"> Imprint </td><td style="padding-left:5px;">01 Nov 2023</td></tr> <tr><td class="formatRecordLabel"> Number of pages </td><td style="padding-left:5px;">11</td></tr>  <tr><td class="formatRecordLabel"> Published in: </td><td style="padding-left:5px;"><a href="http://dx.doi.org/10.1016/j.physletb.2024.138513"><i>Phys. Lett. B</i> 850 (2024) 138513</a> </a></td></tr> <tr><td class="formatRecordLabel"> DOI </td><td style="padding-left:5px;"><a href="http://dx.doi.org/10.1016/j.physletb.2024.138513" title="DOI" target="_blank">10.1016/j.physletb.2024.138513</a> <tr><td class="formatRecordLabel"> Subject category </td><td style="padding-left:5px;">Particle Physics - Experiment ; Particle Physics - Phenomenology</td></tr> <tr><td class="formatRecordLabel"> Accelerator/Facility, Experiment </td><td style="padding-left:5px;"><a href="https://cds.cern.ch/search?p=CERN%20SPS&f=693__a">CERN SPS</a> ; <a href="https://cds.cern.ch/search?p=NA62&f=693__e">NA62</a></td></tr> <tr><td class="formatRecordLabel"> Keywords </td><td style="padding-left:5px;"><a href="https://cds.cern.ch/search?f=keyword&p=flavor%20physics&ln=en">flavor physics</a> ; <a href="https://cds.cern.ch/search?f=keyword&p=QCD&ln=en">QCD</a> ; <a href="https://cds.cern.ch/search?f=keyword&p=exotics&ln=en">exotics</a> ; <a href="https://cds.cern.ch/search?f=keyword&p=branching%20fraction&ln=en">branching fraction</a> ; <a href="https://cds.cern.ch/search?f=keyword&p=experimental%20results&ln=en">experimental results</a> ; <a href="https://cds.cern.ch/search?f=keyword&p=rare%20decay&ln=en">rare decay</a> ; <a href="https://cds.cern.ch/search?f=keyword&p=Chiral%20Perturbation%20Theory&ln=en">Chiral Perturbation Theory</a> ; <a href="https://cds.cern.ch/search?f=keyword&p=hidden%20sector%20mediator&ln=en">hidden sector mediator</a></td></tr> <tr><td class="formatRecordLabel"> Abstract </td><td style="padding-left:5px;">A sample of 3984 candidates of the $K^+ \to \pi^+ \gamma \gamma$ decay, with an estimated background of $291 \pm 14$ events, was collected by the NA62 experiment at CERN during 2017–2018. In order to describe the observed di-photon mass spectrum, the next-to-leading order contribution in chiral perturbation theory was found to be necessary. The decay branching ratio in the full kinematic range is measured to be ($9.61 \pm 0.17) \times 10^{−7}$. The first search for production and prompt decay of an axion-like particle with gluon coupling in the process $K^+ \to \pi^+ a, a \to \gamma \gamma$ is also reported.</td></tr> <tr><td class="formatRecordLabel"> Other source </td><td style="padding-left:5px;"><a href="http://inspirehep.net/record/2718968">Inspire</a></td></tr> <tr><td class="formatRecordLabel"> Copyright/License </td><td style="padding-left:5px;">Preprint: © 2023-2025 CERN (License: <a href="http://creativecommons.org/licenses/by/4.0/">CC-BY-4.0</a>)<br/>Publication: © 2024-2025 The Author (License: <a href="http://creativecommons.org/licenses/by/4.0/">CC BY 4.0</a>), sponsored by <a href="http://scoap3.org">SCOAP³</a></td></tr> <tr><td class="formatRecordLabel"> Submitted by </td><td style="padding-left:5px;"><a href="mailto:brigitte.bloch-devaux@cern.ch">brigitte.bloch-devaux@cern.ch</a></td></tr> </table> <br /><div style="max-width:1024px;margin:auto"><div style="overflow-x:auto;display:inline;width:100%;"><a href="/record/2869421/plots#0"><img style="vertical-align:middle;" src="https://cds.cern.ch/record/2869421/files/na62-sketch2.png" title=" Schematic side view of the NA62 beamline and detector used in 2018." width="200px"/></a> <a href="/record/2869421/plots#1"><img style="vertical-align:middle;" src="https://cds.cern.ch/record/2869421/files/dp_dm_data_colz_z02.png" title=" Reconstructed ($m_{\pi\gamma\gamma}$, $\Delta p$) distributions after the full $K_{\pi\gamma\gamma}$ selection for data (left) and simulated background decay samples (right). The simulated distributions have a common normalisation to the data according to their branching ratios; all plots have the same colour scale. The elliptical selection condition, and the rectangular regions used to obtain the $m_{\pi\gamma\gamma}$ spectrum (Fig.~\ref{fig:mass_plots}) and a control data sample for $K^+\to\pi^+\pi^+\pi^-$ background evaluation~(as discussed in Section~\ref{sec:background}) are shown by solid lines." width="200px"/></a> <a href="/record/2869421/plots#2"><img style="vertical-align:middle;" src="https://cds.cern.ch/record/2869421/files/dp_dm_bkg_z02.png" title=" Reconstructed ($m_{\pi\gamma\gamma}$, $\Delta p$) distributions after the full $K_{\pi\gamma\gamma}$ selection for data (left) and simulated background decay samples (right). The simulated distributions have a common normalisation to the data according to their branching ratios; all plots have the same colour scale. The elliptical selection condition, and the rectangular regions used to obtain the $m_{\pi\gamma\gamma}$ spectrum (Fig.~\ref{fig:mass_plots}) and a control data sample for $K^+\to\pi^+\pi^+\pi^-$ background evaluation~(as discussed in Section~\ref{sec:background}) are shown by solid lines." width="200px"/></a> <a href='/record/2869421/plots'>Show more plots</a></div></div><br /> <br/><div><div style="clear: both;"> </div></div> <script type="text/javascript"> // Initially hide: $(".longCaption").hide(); // Allow to toggle visibility: $(".toggleLongCaption").toggle(function(){ $(this).siblings(".longCaption").show('fast'); var thisElem = $(this); thisElem.text(thisElem.text() === "more" ? "less" : "more"); },function(){ $(this).siblings(".longCaption").hide('fast'); var thisElem = $(this); thisElem.text(thisElem.text() === "more" ? 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