Search for associated production of a Z boson with a single top quark and for tZ flavour-changing interactions in pp collisions at root s=8 TeV
Austrian Federal Ministry of Science, Research and Economy ; Austrian Science Fund ; Belgian Fonds de la Recherche Scientifique ; Fonds voor Wetenschappelijk Onderzoek ; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) ; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) ; Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) ; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) ; Bulgarian Ministry of Education and Science ; CERN ; Chinese Academy of Sciences ; Ministry of Science and Technology ; National Natural Science Foundation of China ; Colombian Funding Agency (COLCIENCIAS) ; Croatian Ministry of Science, Education and Sport ; Croatian Science Foundation ; Research Promotion Foundation, Cyprus ; Secretariat for Higher Education, Science, Technology and Innovation, Ecuador ; Ministry of Education and Research, Estonia ; Estonian Research Council, Estonia ; European Regional Development Fund, Estonia ; Academy of Finland ; Finnish Ministry of Education and Culture ; Helsinki Institute of Physics ; Institut National de Physique Nucleaire et de Physique des Particules / CNRS, France ; Commissariat a l'Energie Atomique et aux Energies Alternatives / CEA, France ; Bundesministerium fur Bildung and Forschung, Germany ; Deutsche Forschungsgemeinschaft, Germany ; Helmholtz-Gemeinschaft Deutscher Forschungszentren, Germany ; General Secretariat for Research and Technology, Greece ; National Scientific Research Foundation, Hungary ; National Innovation Office, Hungary ; Department of Atomic Energy, India ; Department of Science and Technology, India ; Institute for Studies in Theoretical Physics and Mathematics, Iran ; Science Foundation, Ireland ; Istituto Nazionale di Fisica Nucleare, Italy ; Ministry of Science, ICT and Future Planning, Republic of Korea ; National Research Foundation (NRF), Republic of Korea ; Lithuanian Academy of Sciences ; Ministry of Education (Malaysia) ; University of Malaya (Malaysia) ; Mexican Funding Agency (BUAP) ; Mexican Funding Agency (CINVESTAV) ; Mexican Funding Agency (CONACYT) ; Mexican Funding Agency (LNS) ; Mexican Funding Agency (SEP) ; Mexican Funding Agency (UASLP-FAI) ; Ministry of Business, Innovation and Employment, New Zealand ; Pakistan Atomic Energy Commission ; Ministry of Science and Higher Education, Poland ; National Science Centre, Poland ; Fundacao para a Ciencia e a Tecnologia, Portugal ; JINR, Dubna ; Ministry of Education and Science of the Russian Federation ; Federal Agency of Atomic Energy of the Russian Federation ; Russian Academy of Sciences ; Russian Foundation for Basic Research ; Russian Competitiveness Program of NRNU ?MEPhI? ; Ministry of Education, Science and Technological Development of Serbia ; Secretaria de Estado de Investigacion, Desarrollo e Innovacion, Spain ; Programa Consolider-Ingenio, Spain ; Plan de Ciencia, Tecnologia e Innovacion del Principado de Asturias, Spain ; Fondo Europeo de Desarrollo Regional, Spain ; Swiss Funding Agency (ETH Board) ; Swiss Funding Agency (ETH Zurich) ; Swiss Funding Agency (PSI) ; Swiss Funding Agency (SNF) ; Swiss Funding Agency (UniZH) ; Swiss Funding Agency (Canton Zurich) ; Swiss Funding Agency (SER) ; Ministry of Science and Technology, Taipei ; Thailand Center of Excellence in Physics ; Institute for the Promotion of Teaching Science and Technology of Thailand ; Special Task Force for Activating Research ; National Science and Technology Development Agency of Thailand ; Scientific and Technical Research Council of Turkey ; Turkish Atomic Energy Authority ; National Academy of Sciences of Ukraine ; State Fund for Fundamental Researches, Ukraine ; Science and Technology Facilities Council, U.K. ; U.S. Department of Energy ; U.S. National Science Foundation ; Marie-Curie programme (European Union) ; European Research Council (European Union) ; EPLANET (European Union) ; Leventis Foundation ; A. P. Sloan Foundation ; Alexander von Humboldt Foundation ; Belgian Federal Science Policy Office ; Fonds pour la Formation a la Recherche dans l'Industrie et dans l'Agriculture (FRIA-Belgium) ; Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium) ; Ministry of Education, Youth and Sports (MEYS) of the Czech Republic ; Council of Science and Industrial Research, India ; HOMING PLUS programme of the Foundation for Polish Science from European Union ; Regional Development Fund ; Mobility Plus programme of the Ministry of Science and Higher Education ; National Science Center (Poland) ; National Priorities Research Program by Qatar National Research Fund ; Programa Clarin-COFUND del Principado de Asturias ; Thalis programme - EU-ESF ; Aristeia programme - EU-ESF ; Greek NSRF ; Rachadapisek Sompot Fund for Postdoctoral Fellowship (Thailand) ; Chulalongkorn University (Thailand) ; Chulalongkorn Academic into Its 2nd Century Project Advancement Project (Thailand) ; Welch Foundation ; Estonian Research Council, Estonia: IUT23-4 ; Estonian Research Council, Estonia: IUT23-6 ; National Science Center (Poland): Harmonia 2014/14/M/ST2/00428 ; National Science Center (Poland): Opus 2014/13/B/ST2/02543 ; National Science Center (Poland): 2014/15/B/ST2/03998 ; National Science Center (Poland): 2015/19/B/ST2/02861 ; National Science Center (Poland): Sonata-bis 2012/07/E/ST2/01406 ; Welch Foundation: C-1845 ; A search for the production of a single top quark in association with a Z boson is presented, both to identify the expected standard model process and to search for flavour changing neutral current interactions. The data sample corresponds to an integrated luminosity of 19.7 fb(-1) recorded by the CMS experiment at the LHC in proton-proton collisions at root s = 8 TeV. Final states with three leptons (electrons or muons) and at least one jet are investigated. An events yield compatible with tZq standard model production is observed, and the corresponding cross section is measured to be sigma(pp -> tZq -> lvbl(+)l(-) q) = 10(-7)(+8) fb with a significance of 2.4 standard deviations. No presence of flavour-changing neutral current production of tZq is observed. Exclusion limits at 95% confidence level on the branching fractions of a top quark decaying to a Z boson and an up or a charm quark are found to be B(t -> Zu) Zc) < 0.049%.