Search for lepton-flavour-violating decays of the Higgs boson

Abstract

The first direct search for lepton-flavour-violating decays of the recently discovered Higgs boson (H) is described. The search is performed in the H???e and H???h channels, where ?e and ?h are tau leptons reconstructed in the electronic and hadronic decay channels, respectively. The data sample used in this search was collected in pp collisions at a centre-of-mass energy of s=8 TeV with the CMS experiment at the CERN LHC and corresponds to an integrated luminosity of 19.7 fb?1. The sensitivity of the search is an order of magnitude better than the existing indirect limits. A slight excess of signal events with a significance of 2.4 standard deviations is observed. The p-value of this excess at MH=125 GeV is 0.010. The best fit branching fraction is B(H???)=(0.84?0.37 +0.39)%. A constraint on the branching fraction, B(H???)>1.51% at 95% confidence level is set. This limit is subsequently used to constrain the ?–? Yukawa couplings to be less than 3.6×10?3 ; California Earthquake Authority Fonds pour la Formation à la Recherche dans l'Industrie et dans l'Agriculture Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro State Fund for Fundamental Research of Ukraine: Ukraine CS Fund: Croatia Fuel Cell Technologies Program Joint Institute for Nuclear Research Ministry of Education - Singapore Pakistan Atomic Energy Commission: Pakistan Consejo Nacional de Ciencia y Tecnología National Science and Technology Development Agency: Thailand Ministry for Business Innovation and Employment Institute for Research in Fundamental Sciences Fundacja na rzecz Nauki Polskiej Foundation for Promotion of Material Science and Technology of Japan: Taipei Hispanics in Philanthropy Korea Research Council for Industrial Science and Technology Compagnia di San Paolo California Department of Fish and Game National Research Foundation Secretaría de Estado de Investigación, Desarrollo e Innovación Qatar National Research Fund Ministry of Science ICT and Future Planning Canadian Mathematical Society A.G. Leventis Foundation U.S. Department of Energy Academy of Finland Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Ministerio de Educación y Cultura Türkiye Atom Enerjisi Kurumu Research Promotion Foundation: Cyprus National Science Foundation Science and Technology Facilities Council Human Growth Foundation Austrian Science Fund Fundação de Amparo à Pesquisa do Estado de São Paulo Secretaría de Educación Pública Bundesministerium für Wissenschaft, Forschung und Wirtschaft Fonds De La Recherche Scientifique - FNRS National Academy of Sciences of Ukraine Bundesministerium für Bildung und Forschung National Natural Science Foundation of China European Regional Development Fund Instituto Nazionale di Fisica Nucleare Hungarian Scientific Research Fund Department of Atomic Energy, Government of India Universidade de Macau Rochester Academy of Science Department of Science and Technology, Government of Rajasthan Conselho Nacional de Desenvolvimento Científico e Tecnológico ?????????? ???? ??????????????? ???????????? (????) Canadian Anesthesiologists' Society Belgian Federal Science Policy Office Agentschap voor Innovatie door Wetenschap en Technologie Departamento Administrativo de Ciencia, Tecnología e Innovación Alexander von Humboldt-Stiftung Ministerstvo Školství, Mláde?e a T?lov?chovy National Institutes of Health: Hungary European Regional Development Fund Ministerstvo Školství, Mláde?e a T?lov?chovy CERN Ministero dell'Istruzione, dell'Università e della Ricerca: 20108T4XTM Serbia NSC General Secretariat for Research and Technology Fonds Wetenschappelijk Onderzoek European Research Council Santa Fe Institute Ministry of Education and Science Louisiana Academy of Sciences ; We congratulate our colleagues in the CERN accelerator departments for the excellent performance of the LHC and thank the technical and administrative staffs at CERN and at other CMS institutes for their contributions to the success of the CMS effort. In addition, we gratefully acknowledge the computing centres and personnel of the Worldwide LHC Computing Grid for delivering so effectively the computing infrastructure essential to our analyses. Finally, we acknowledge the enduring support for the construction and operation of the LHC and the CMS detector provided by the following funding agencies: BMWFW and FWF (Austria); FNRS and FWO (Belgium); CNPq , CAPES , FAPERJ , and FAPESP (Brazil); MES (Bulgaria); CERN ; CAS , MoST , and NSFC (China); COLCIENCIAS (Colombia); MSES and CSF (Croatia); RPF (Cyprus); MoER , ERC IUT and ERDF (Estonia); Academy of Finland , MEC , and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF , DFG , and HGF (Germany); GSRT (Greece); OTKA and NIH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); MSIP and NRF (Republic of Korea); LAS (Lithuania); MOE and UM (Malaysia); CINVESTAV , CONACYT , SEP , and UASLP-FAI (Mexico); MBIE (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Dubna); MON , RosAtom , RAS and RFBR (Russia); MESTD (Serbia); SEIDI and CPAN (Spain); Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter , IPST , STAR and NSTDA (Thailand); TUBITAK and TAEK (Turkey); NASU and SFFR (Ukraine); STFC (United Kingdom); DOE and NSF (USA). Individuals have received support from the Marie-Curie programme and the European Research Council and EPLANET (European Union); the Leventis Foundation ; the A.P. Sloan Foundation ; the Alexander von Humboldt Foundation ; the Belgian Federal Science Policy Office ; the Fonds pour la Formation à la Recherche dans l'Industrie et dans l'Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium); the Ministry of Education, Youth and Sports ( MEYS ) of the Czech Republic; the Council of Science and Industrial Research, India ; the HOMING PLUS programme of Foundation for Polish Science , cofinanced from European Union , Regional Development Fund ; the Compagnia di San Paolo (Torino); the Consorzio per la Fisica (Trieste); MIUR project 20108T4XTM (Italy); the Thalis and Aristeia programmes cofinanced by EU-ESF and the Greek NSRF ; and the National Priorities Research Program by Qatar National Research Fund .