The CMS experiment at the CERN LHC

Este artículo fue en colaboración con otras Universidades en la que participaron alrededor de 2300 autores.

Search for pair-produced resonances decaying to jet pairs in proton–proton collisions at s=8 TeV

Results are reported of a general search for pair production of heavy resonances decaying to pairs of hadronic jets in events with at least four jets. The study is based on up to 19.4 fb?1 of integrated luminosity from proton–proton collisions at a center-of-mass energy of 8 TeV, recorded with the CMS detector at the LHC. Limits are determined on the production of scalar top quarks (top squarks) in the framework of R-parity violating supersymmetry and on the production of color-octet vector bosons (colorons). First limits at the LHC are placed on top squark production for two scenarios. The first assumes decay to a bottom quark and a light-flavor quark and is excluded for masses between 200 and 385 GeV, and the second assumes decay to a pair of light-flavor quarks and is excluded for masses between 200 and 350 GeV at 95% confidence level. Previous limits on colorons decaying to light-flavor quarks are extended to exclude masses from 200 to 835 GeVCalifornia Earthquake Authority Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture European Regional Development Fund State Fund for Fundamental Research of Ukraine: Ukraine Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro CS Fund: Croatia Fuel Cell Technologies Program Bangladesh Council of Scientific and Industrial Research Joint Institute for Nuclear Research Ministry of Education - Singapore Pakistan Atomic Energy Commission: Pakistan Consejo Nacional de Ciencia y Tecnología Ministry for Business Innovation and Employment National Science and Technology Development Agency: Thailand Institute for Research in Fundamental Sciences Ministry of Science and Technology Foundation for Promotion of Material Science and Technology of Japan: Taipei Hispanics in Philanthropy California Department of Fish and Game Compagnia di San Paolo Qatar National Research Fund National Research Foundation Secretaría de Estado de Investigación, Desarrollo e Innovación Ministry of Science ICT and Future Planning Canadian Mathematical Society A.G. Leventis Foundation U.S. Department of Energy Türkiye Bilimsel ve Teknolojik Araştirma Kurumu Academy of Finland Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Türkiye Atom Enerjisi Kurumu Ministerio de Educación y Cultura 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 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 Agentschap voor Innovatie door Wetenschap en Technologie Belgian Federal Science Policy Office Departamento Administrativo de Ciencia, Tecnología e Innovación Alexander von Humboldt-Stiftung Ministerstvo Školství, Mláde?e a T?lov?chovy European Commission National Institutes of Health: Hungary CERN Ministerstvo Školství, Mláde?e a T?lov?chovy European Regional Development Fund 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 A.P. Giannini FoundationWe 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 centers 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); TÜBITAK and TAEK (Turkey); NASU and SFFR (Ukraine); STFC (United Kingdom); DOE and NSF (USA). Individuals have received support from the Marie-Curie program 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 Scientific and Industrial Research , India; the HOMING PLUS program 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 programs cofinanced by EU-ESF and the Greek NSRF ; and the National Priorities Research Program by Qatar National Research Fund

Search for the production of dark matter in association with top-quark pairs in the single-lepton final state in proton-proton collisions at ?S= 8TeV

A search is presented for particle dark matter produced in association with a pair of top quarks in pp collisions at a centre-of-mass energy of ?S= 8TeV. The data were collected with the CMS detector at the LHC and correspond to an integrated luminosity of 19.7 fb?1. This search requires the presence of one lepton, multiple jets, and large missing transverse energy. No excess of events is found above the SM expectation, and upper limits are derived on the production cross section. Interpreting the findings in the context of a scalar contact interaction between fermionic dark matter particles and top quarks, lower limits on the interaction scale are set. These limits are also interpreted in terms of the dark matter-nucleon scattering cross sections for the spin-independent scalar operator and they complement direct searches for dark matter particles in the low mass regionScience and Technology Facilities Council: CMS Science and Technology Facilities Council: GRIDPP Science and Technology Facilities Council: ST/I005912/1 Science and Technology Facilities Council: ST/I505580/1 Science and Technology Facilities Council: ST/J004901/1 Science and Technology Facilities Council: ST/J005665/1 Science and Technology Facilities Council: ST/J50094X/1 Science and Technology Facilities Council: ST/K001256/1 Science and Technology Facilities Council: ST/K001604/1 Science and Technology Facilities Council: ST/K001639/1 Science and Technology Facilities Council: ST/K003542/1 Science and Technology Facilities Council: ST/K003844/1 Science and Technology Facilities Council: ST/L005603/1 Science and Technology Facilities Council: ST/L00609X/1 Science and Technology Facilities Council: ST/M004775/1 Science and Technology Facilities Council: ST/M005356/1 Science and Technology Facilities Council: ST/N000250/

Measurement of the W boson helicity in events with a single reconstructed top quark in pp collisions at ?s = 8 TeV

A measurement of the W boson helicity is presented, where the W boson originates from the decay of a top quark produced in pp collisions. The event selection, optimized for reconstructing a single top quark in the final state, requires exactly one isolated lepton (muon or electron) and exactly two jets, one of which is likely to originate from the hadronization of a bottom quark. The analysis is performed using data recorded at a center-of-mass energy of 8 TeV with the CMS detector at the CERN LHC in 2012. The data sample corresponds to an integrated luminosity of 19.7 fb?1. The measured helicity fractions are FL = 0.298 ± 0.028 (stat) ± 0.032(syst), F0 = 0.720 ± 0.039 (stat) ± 0.037(syst), and FR = ?0.018 ± 0.019 (stat) ± 0.011(syst). These results are used to set limits on the real part of the tWb anomalous couplings, gL and g

Search for physics beyond the standard model in events with two leptons, jets, and missing transverse momentum in pp collisions at ?S= 8 TeV

Abstract: A search is presented for physics beyond the standard model in final states with two opposite-sign same-flavor leptons, jets, and missing transverse momentum. The data sample corresponds to an integrated luminosity of 19.4 fb ?1 of proton-proton collisions at ?S= 8 TeV collected with the CMS detector at the CERN LHC in 2012. The analysis focuses on searches for a kinematic edge in the invariant mass distribution of the oppositesign same-flavor lepton pair and for final states with an on-shell Z boson. The observations are consistent with expectations from standard model processes and are interpreted in terms of upper limits on the production of supersymmetric particle

Search for stealth supersymmetry in events with jets, either photons or leptons, and low missing transverse momentum in pp collisions at 8 TeV

The results of a search for new physics in final states with jets, either photons or leptons, and low missing transverse momentum are reported. The study is based on a sample of proton-proton collisions collected at a center-of-mass energy s=8 TeV with the CMS detector in 2012. The integrated luminosity of the sample is 19.7 fb-1. Many models of new physics predict the production of events with jets, electroweak gauge bosons, and little or no missing transverse momentum. Examples include stealth models of supersymmetry (SUSY), which predict a hidden sector at the electroweak energy scale in which SUSY is approximately conserved. The data are used to search for stealth SUSY signatures in final states with either two photons or an oppositely charged electron and muon. No excess is observed with respect to the standard model expectation, and the results are used to set limits on squark pair production in the stealth SUSY frameworkScience and Technology Facilities Council: CMS Science and Technology Facilities Council: GRIDPP Science and Technology Facilities Council: ST/I005912/1 Science and Technology Facilities Council: ST/I505580/1 Science and Technology Facilities Council: ST/J004901/1 Science and Technology Facilities Council: ST/J005665/1 Science and Technology Facilities Council: ST/J50094X/1 Science and Technology Facilities Council: ST/K001256/1 Science and Technology Facilities Council: ST/K001604/1 Science and Technology Facilities Council: ST/K001639/1 Science and Technology Facilities Council: ST/K003542/1 Science and Technology Facilities Council: ST/K003844/1 Science and Technology Facilities Council: ST/L005603/1 Science and Technology Facilities Council: ST/L00609X/1 Science and Technology Facilities Council: ST/M004775/1 Science and Technology Facilities Council: ST/M005356/1 Science and Technology Facilities Council: ST/N000250/

Search for physics beyond the standard model in dilepton mass spectra in proton-proton collisions at ?s=8TeV

Abstract: Dimuon and dielectron mass spectra, obtained from data resulting from proton-proton collisions at 8 TeV and recorded by the CMS experiment, are used to search for both narrow resonances and broad deviations from standard model predictions. The data correspond to an integrated luminosity of 20.6 (19.7) fb ?1 for the dimuon (dielectron) channel. No evidence for non-standard-model physics is observed and 95% confidence level limits are set on parameters from a number of new physics models. The narrow resonance analyses exclude a Sequential Standard Model Z SSM ? resonance lighter than 2.90 TeV, a superstring-inspired Z ? ? lighter than 2.57 TeV, and Randall-Sundrum Kaluza-Klein gravitons with masses below 2.73, 2.35, and 1.27 TeV for couplings of 0.10, 0.05, and 0.01, respectively. A notable feature is that the limits have been calculated in a model-independent way to enable straightforward reinterpretation in any model predicting a resonance structure. The observed events are also interpreted within the framework of two non-resonant analyses: one based on a large extra dimensions model and one based on a quark and lepton compositeness model with a left-left isoscalar contact interaction. Lower limits are established on M S , the scale characterizing the onset of quantum gravity, which range from 4.9 to 3.3 TeV, where the number of additional spatial dimensions varies from 3 to 7. Similarly, lower limits on ?, the energy scale parameter for the contact interaction, are found to be 12.0 (15.2) TeV for destructive (constructive) interference in the dimuon channel and 13.5 (18.3) TeV in the dielectron channel.[Figure not available: see fulltext.] © 2015, The Author(s)

Performance of electron reconstruction and selection with the CMS detector in proton-proton collisions at ?s = 8 TeV

The performance and strategies used in electron reconstruction and selection at CMS are presented based on data corresponding to an integrated luminosity of 19.7 fb-1, collected in proton-proton collisions at ?s = 8 TeV at the CERN LHC. The paper focuses on prompt isolated electrons with transverse momenta ranging from about 5 to a few 100 GeV. A detailed description is given of the algorithms used to cluster energy in the electromagnetic calorimeter and to reconstruct electron trajectories in the tracker. The electron momentum is estimated by combining the energy measurement in the calorimeter with the momentum measurement in the tracker. Benchmark selection criteria are presented, and their performances assessed using Z, , and J/? decays into e+ + e- pairs. The spectra of the observables relevant to electron reconstruction and selection as well as their global efficiencies are well reproduced by Monte Carlo simulations. The momentum scale is calibrated with an uncertainty smaller than 0.3%. The momentum resolution for electrons produced in Z boson decays ranges from 1.7 to 4.5%, depending on electron pseudorapidity and energy loss through bremsstrahlung in the detector materia

Search for heavy Majorana neutrinos in ?±?± + jets events in proton-proton collisions at s=8 TeV

A search is performed for heavy Majorana neutrinos (N) using an event signature defined by two muons of the same charge and two jets (?±?±jj). The data correspond to an integrated luminosity of 19.7 fb-1 of proton-proton collisions at a center-of-mass energy of 8 TeV, collected with the CMS detector at the CERN LHC. No excess of events is observed beyond the expected standard model background and upper limits are set on |V?N|2 as a function of Majorana neutrino mass mN for masses in the range of 40-500 GeV, where V?N is the mixing element of the heavy neutrino with the standard model muon neutrino. The limits obtained are |V?N|2>0.00470 for mN=90 GeV, |V?N|2>0.0123 for mN=200 GeV, and |V?N|2>0.583 for mN=500 GeV. These results extend considerably the regions excluded by previous direct searchesCalifornia Earthquake Authority Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture European Regional Development Fund State Fund for Fundamental Research of Ukraine: Ukraine Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro 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 Ministry for Business Innovation and Employment National Science and Technology Development Agency: Thailand Institute for Research in Fundamental Sciences Ministry of Science and Technology 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 Türkiye Atom Enerjisi Kurumu Ministerio de Educación y Cultura 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 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 ?????????? ???? ??????????????? ???????????? (????) Belgian Federal Science Policy Office Agentschap voor Innovatie door Wetenschap en Technologie Canadian Anesthesiologists' Society Alexander von Humboldt-Stiftung Departamento Administrativo de Ciencia, Tecnología e Innovación European Commission Ministerstvo Školství, Mláde?e a T?lov?chovy National Institutes of Health: Hungary CERN Ministerstvo Školství, Mláde?e a T?lov?chovy European Regional Development Fund Ministero dell’Istruzione, dell’Università e della Ricerca: 20108T4XTM Serbia NSC General Secretariat for Research and Technology European Research Council Fonds Wetenschappelijk Onderzoek Santa Fe Institute Ministry of Education and Science Louisiana Academy of SciencesWe would like to thank Juan Antonio Aguliar-Saavedra, Francisco del Aguila, and Tao Han for assistance with Monte Carlo generators and calculations of the heavy neutrino branching fractions, as well as for advice on the theoretical interpretations of our results. 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 centers 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 program 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 program 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 programs cofinanced by EU-ESF and the Greek NSRF; and the National Priorities Research Program by Qatar National Research Fund