Showing papers by "Yueh-Feng Liu published in 2016"
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TL;DR: In this article, a search for a high-mass Higgs boson in the,,, and decay modes using the ATLAS detector at the CERN Large Hadron Collider is presented.
Abstract: A search is presented for a high-mass Higgs boson in the , , , and decay modes using the ATLAS detector at the CERN Large Hadron Collider. The search uses proton-proton collision data at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.3 fb. The results of the search are interpreted in the scenario of a heavy Higgs boson with a width that is small compared with the experimental mass resolution. The Higgs boson mass range considered extends up to for all four decay modes and down to as low as 140 , depending on the decay mode. No significant excess of events over the Standard Model prediction is found. A simultaneous fit to the four decay modes yields upper limits on the production cross-section of a heavy Higgs boson times the branching ratio to boson pairs. 95 % confidence level upper limits range from 0.53 pb at GeV to 0.008 pb at GeV for the gluon-fusion production mode and from 0.31 pb at GeV to 0.009 pb at GeV for the vector-boson-fusion production mode. The results are also interpreted in the context of Type-I and Type-II two-Higgs-doublet models.
241 citations
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TL;DR: In this article, the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cb vertical bar was determined based on 711 fb(-1) of e(+)e(-) -> Upsilon(4S) data recorded by the Belle detector and containing 772 x 10(6) B (B) over bar pairs.
Abstract: We present a determination of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cb vertical bar using the decay B -> Dl nu(l) (l = e,mu) based on 711 fb(-1) of e(+)e(-) -> Upsilon(4S) data recorded by the Belle detector and containing 772 x 10(6) B (B) over bar pairs. One B meson in the event is fully reconstructed in a hadronic decay mode, while the other, on the signal side, is partially reconstructed from a charged lepton and either a D+ or D-0 meson in a total of 23 hadronic decay modes. The isospin-averaged branching fraction of the decay B -> Dl nu(l) is found to be B(B-0 -> D(-)l(vertical bar)nu(l)) = (2.31 +/- 0.03(stat) +/- 0.11(syst))%. Analyzing the differential decay rate as a function of the hadronic recoil with the parametrization of Caprini, Lellouch, and Neubert and using the form-factor prediction G(1) = 1.0541 +/- 0.0083 calculated by FNAL/MILC, we obtain eta(EW)vertical bar V-cb vertical bar = (40.12 +/- 1.34) x 10(-3), where eta(EW) is the electroweak correction factor. Alternatively, assuming the model-independent form-factor parametrization of Boyd, Grinstein, and Lebed and using lattice QCD data from the FNAL/MILC and HPQCD collaborations, we find eta(EW)vertical bar V-cb vertical bar = (41.10 +/- 1.14) x 10(-3).
142 citations
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TL;DR: In this paper, the results on two-particle angular correlations for charged particles produced in pp collisions at a center-of-mass energy of 13 TeV were presented, and the data were taken with the CMS detector at the LHC.
Abstract: Results on two-particle angular correlations for charged particles produced in pp collisions at a center-of-mass energy of 13 TeV are presented. The data were taken with the CMS detector at the LHC and correspond to an integrated luminosity of about 270 nb^(−1). The correlations are studied over a broad range of pseudorapidity (|η| 2.0), near-side (Δϕ≈0) structure emerges in the two-particle Δη–Δϕ correlation functions. The magnitude of the correlation exhibits a pronounced maximum in the range 1.0
139 citations
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Vardan Khachatryan1, Albert M. Sirunyan1, Armen Tumasyan1, Wolfgang Adam2 +2287 more•Institutions (178)
TL;DR: In this article, the angular distribution and the differential branching fraction of the decay B0 to K*0(892) mu mu are studied using data corresponding to an integrated luminosity of 20.5 inverse femtobarns collected with the CMS detector at the LHC in pp collisions at sqrt(s) = 8 TeV.
129 citations
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Vardan Khachatryan, Albert M. Sirunyan, Armen Tumasyan, Wolfgang Adam1 +2369 more•Institutions (184)
TL;DR: In this article, a search for fermionic top quark partners T of charge 2/3 was carried out in proton-proton collisions corresponding to an integrated luminosity of 19.7 inverse femtobarns collected at a center-of-mass energy of sqrt(s) = 8 TeV with the CMS detector at the LHC.
Abstract: A search for fermionic top quark partners T of charge 2/3 is presented. The search is carried out in proton-proton collisions corresponding to an integrated luminosity of 19.7 inverse femtobarns collected at a center-of-mass energy of sqrt(s) = 8 TeV with the CMS detector at the LHC. The T quarks are assumed to be produced strongly in pairs and can decay into tH, tZ, and bW. The search is performed in five exclusive channels: a single-lepton channel, a multilepton channel, two all-hadronic channels optimized either for the bW or the tH decay, and one channel in which the Higgs boson decays into two photons. The results are found to be compatible with the standard model expectations in all the investigated final states. A statistical combination of these results is performed and lower limits on the T quark mass are set. Depending on the branching fractions, lower mass limits between 720 and 920 GeV at 95% confidence level are found. These are among the strongest limits on vector-like T quarks obtained to date.
122 citations
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Vardan Khachatryan1, Robin Erbacher2, C. A. Carrillo Montoya3, Wagner Carvalho4 +2303 more•Institutions (174)
TL;DR: In this paper, the authors describe the algorithms used by the CMS experiment to reconstruct and identify tau to hadrons + tau neutrino decays during Run 1 of the LHC.
Abstract: This paper describes the algorithms used by the CMS experiment to reconstruct and identify tau to hadrons + tau neutrino decays during Run 1 of the LHC. The performance of the algorithms is studied in proton-proton collisions recorded at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 inverse femtobarns. The algorithms achieve an identification efficiency of 50-60%, with misidentification rates for quark and gluon jets, electrons, and muons between per mille and per cent levels.
112 citations
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Vardan Khachatryan1, Albert M. Sirunyan1, Armen Tumasyan1, Wolfgang Adam +2311 more•Institutions (180)
TL;DR: In this article, a search for a heavy scalar boson H decaying into a pair of lighter standard-model-like 125 GeV Higgs bosons h and an h boson decaying into an H boson was performed on a dataset corresponding to an integrated luminosity of 19.7 inverse femtobarns of pp collision data at a centre-of-mass energy of 8 TeV.
102 citations
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Vardan Khachatryan1, Robin Erbacher1, Camilo Andres Carrillo Montoya1, Wagner Carvalho2 +2332 more•Institutions (8)
TL;DR: In this article, a search for the production of a heavy B quark, having electric charge −1/3 and vector couplings to W, Z, and H bosons, is carried out using proton-proton collision data recorded at the CERN LHC by the CMS experiment, corresponding to an integrated luminosity of 19.7
Abstract: A search for the production of a heavy B quark, having electric charge −1/3 and vector couplings to W, Z, and H bosons, is carried out using proton-proton collision data recorded at the CERN LHC by the CMS experiment, corresponding to an integrated luminosity of 19.7 fb^(−1). The B quark is assumed to be pair produced and to decay in one of three ways: to tW, bZ, or bH. The search is carried out in final states with one, two, and more than two charged leptons, as well as in fully hadronic final states. Each of the channels in the exclusive final-state topologies is designed to be sensitive to specific combinations of the B quark-antiquark pair decays. The observed event yields are found to be consistent with the standard model expectations in all the final states studied. A statistical combination of these results is performed, and upper limits are set on the cross section of the strongly produced B quark-antiquark pairs as a function of the B quark mass. Lower limits on the B quark mass between 740 and 900 GeV are set at a 95% confidence level, depending on the values of the branching fractions of the B quark to tW, bZ, and bH. Overall, these limits are the most stringent to date.
89 citations
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TL;DR: In this article, a search for the production of two Higgs bosons in final states containing two photons and two bottom quarks is presented, and upper limits are set at 95% confidence level on the production cross section of new particles and compared to the prediction for the existence of a warped extra dimension.
Abstract: A search is presented for the production of two Higgs bosons in final states containing two photons and two bottom quarks. Both resonant and nonresonant hypotheses are investigated. The analyzed data correspond to an integrated luminosity of 19.7 fb^(−1) of proton-proton collisions at √s = 8 TeV collected with the CMS detector. Good agreement is observed between data and predictions of the standard model (SM). Upper limits are set at 95% confidence level on the production cross section of new particles and compared to the prediction for the existence of a warped extra dimension. When the decay to two Higgs bosons is kinematically allowed, assuming a mass scale Λ_R = 1 TeV for the model, the data exclude a radion scalar at masses below 980 GeV. The first Kaluza-Klein excitation mode of the graviton in the RS1 Randall-Sundrum model is excluded for masses between 325 and 450 GeV. An upper limit of 0.71 pb is set on the nonresonant two-Higgs-boson cross section in the SM-like hypothesis. Limits are also derived on nonresonant production assuming anomalous Higgs-boson couplings.
89 citations
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Vardan Khachatryan, Albert M. Sirunyan, Armen Tumasyan, Wolfgang Adam1 +2327 more•Institutions (182)
TL;DR: In this article, a search for a massive resonance decaying into a standard-model-like Higgs boson (H) and a W or Z boson is reported, in which the decay products of Higgs, W and Z bosons at high Lorentz boost are contained within single reconstructed jets.
Abstract: A search for a massive resonance decaying into a standard- model-like Higgs boson (H) and a W or Z boson is reported. The analysis is performed on a data sample corresponding to an integrated luminosity of 19.7 inverse femtobarns, collected in proton-proton collisions at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC. Signal events, in which the decay products of Higgs, W, or Z bosons at high Lorentz boost are contained within single reconstructed jets, are identified using jet substructure techniques, including the tagging of b hadrons. This is the first search for heavy resonances decaying into HW or HZ resulting in an all-jet final state, as well as the first application of jet substructure techniques to identify H to WW* to 4q decays at high Lorentz boost. No significant signal is observed and limits are set at 95% confidence level on the production cross section of W' and Z' in a model with mass-degenerate charged and neutral spin-1 resonances. Resonance masses are excluded for W' in the interval [1.0, 1.6] TeV, for Z' in the intervals [1.0, 1.1] and [1.3, 1.5] TeV, and for mass-degenerate W' and Z' in the interval [1.0, 1.7] TeV.
85 citations
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Vardan Khachatryan1, Albert M. Sirunyan1, Armen Tumasyan1, Wolfgang Adam +2292 more•Institutions (142)
TL;DR: In this article, a measurement of the W boson pair production cross section in proton-proton collisions at √s = 8 TeV is presented, consistent with the standard model prediction.
Abstract: A measurement of the W boson pair production cross section in proton-proton collisions at √s = 8 TeV is presented. The data collected with the CMS detector at the LHC correspond to an integrated luminosity of 19.4 fb^(-1). The W^+W^− candidates are selected from events with two charged leptons, electrons or muons, and large missing transverse energy. The measured W^+W^− cross section is 60.1 ± 0.9(stat) ± 3.2 (exp) ± 3.1(theo)±1.6 (lumi)\,pb = 60.1 ± 4.8\,pb60.1 ± 0.9 (stat) ±3.2 (exp)±3.1 (theo) ± 1.6 (lumi)\,pb = 60.1 ± 4.8\, pb, consistent with the standard model prediction. The W^+W^− cross sections are also measured in two different fiducial phase space regions. The normalized differential cross section is measured as a function of kinematic variables of the final-state charged leptons and compared with several perturbative QCD predictions. Limits on anomalous gauge couplings associated with dimension-six operators are also given in the framework of an effective field theory. The corresponding 95 % confidence level intervals are −5.7
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TL;DR: The algorithms used by the ATLAS Collaboration to reconstruct and identify prompt photons are described and the results are compared to the predictions from a simulation of the detector response, after correcting the electromagnetic shower momenta in the simulation for the average differences observed with respect to data.
Abstract: The algorithms used by the ATLAS Collaboration to reconstruct and identify prompt photons are described. Measurements of the photon identification efficiencies are reported, using 4.9 fb$^{-1}$ of $pp$ collision data collected at the LHC at $\sqrt{s} = 7$ TeV and 20.3 fb$^{-1}$ at $\sqrt{s} = 8$ TeV. The efficiencies are measured separately for converted and unconverted photons, in four different pseudo rapidity regions, for transverse momenta between 10 GeV and 1.5 TeV. The results from the combination of three data-driven techniques are compared to the predictions from a simulation of the detector response, after correcting the electromagnetic shower momenta in the simulation for the average differences observed with respect to data. Data-to-simulation efficiency ratios used as correction factors in physics measurements are determined to account for the small residual efficiency differences. These factors are measured with uncertainties between 0.5% and 10% in 7 TeV data and between 0.5% and 3% in 8 TeV data, depending on the photon transverse momentum and pseudorapidity.
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Vardan Khachatryan1, Albert M. Sirunyan1, Armen Tumasyan1, Wolfgang Adam2 +2336 more•Institutions (191)
TL;DR: In this paper, a search for exclusive or quasi-exclusive γγ → W+W− production, via pp → p(*)W+W+p(*) → p (*)μ±e∓p(*) at √s=8 TeV, is reported using data corresponding to an integrated luminosity of 19.7 fb^(−1).
Abstract: A search for exclusive or quasi-exclusive γγ → W+W− production, via pp → p(*)W+W−p(*) → p(*)μ±e∓p(*) at √s=8 TeV, is reported using data corresponding to an integrated luminosity of 19.7 fb^(−1). Events are selected by requiring the presence of an electron-muon pair with large transverse momentum pT(μ±e∓) > 30 GeV, and no associated charged particles detected from the same vertex. The 8 TeV results are combined with the previous 7 TeV results (obtained for 5.05 fb^(−1) of data). In the signal region, 13 (2) events are observed over an expected background of 3.9 ± 0.6 (0.84 ± 0.15) events for 8 (7) TeV, resulting in a combined excess of 3.4σ over the background-only hypothesis. The observed yields and kinematic distributions are compatible with the standard model prediction for exclusive and quasi-exclusive γγ → W+W− production. Upper limits on the anomalous quartic gauge coupling operators a_(0,C)^W (dimension-6) and f_(M0,1,2,3) (dimension-8), the most stringent to date, are derived from the measured dilepton transverse momentum spectrum.
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Vardan Khachatryan, Albert M. Sirunyan, Armen Tumasyan, Wolfgang Adam1 +2293 more•Institutions (147)
TL;DR: The authors of as discussed by the authors 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); COLCIEN-CIAS (Colombia); MSES and CSF (Croatia); RPF (
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Vardan Khachatryan1, Albert M. Sirunyan1, Armen Tumasyan1, Wolfgang Adam2 +2333 more•Institutions (172)
Abstract: A measurement is presented of differential cross sections for the Higgs boson (H) production in pp collisions at sqrt(s)=8 TeV. The analysis exploits the H to gamma gamma decay in data corresponding to an integrated luminosity of 19.7 inverse femtobarns collected by the CMS experiment at the LHC. The cross section is measured as a function of the kinematic properties of the diphoton system and of the associated jets. Results corrected for detector effects are compared with predictions at next-to-leading order and next-to-next-to-leading order in perturbative quantum chromodynamics, as well as with predictions beyond the standard model. For isolated photons with pseudorapidities abs(eta) 1/3 and >1/4, the total fiducial cross section is 32 +/- 10 fb.
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Vardan Khachatryan1, Albert M. Sirunyan1, Armen Tumasyan1, Wolfgang Adam +2358 more•Institutions (190)
TL;DR: In this paper, the authors acknowledge the enduring support for the construction and operation of the LHC and the CMS detector provided by the following funding agencies: Austria, Belgium, the Netherlands, and the United States National Science Foundation.
Abstract: Finally, we acknowledge the enduring support for the construction and operation
of the LHC and the CMS detector provided by the following funding agencies: the Austrian
Federal Ministry of Science, Research and Economy and the Austrian Science Fund; the
Belgian Fonds de la Recherche Scienti que, and Fonds voor Wetenschappelijk Onderzoek;
the Brazilian Funding Agencies (CNPq, CAPES, FAPERJ, and FAPESP); the Bulgarian
Ministry of Education and Science; CERN; the Chinese Academy of Sciences, Ministry of
Science and Technology, and National Natural Science Foundation of China; the Colombian
Funding Agency (COLCIENCIAS); the Croatian Ministry of Science, Education and Sport,
and the Croatian Science Foundation; the Research Promotion Foundation, Cyprus; the
Ministry of Education and Research, Estonian Research Council via IUT23-4 and IUT23-
6 and European Regional Development Fund, Estonia; the Academy of Finland, Finnish
Ministry of Education and Culture, and Helsinki Institute of Physics; the Institut National
de Physique Nucl eaire et de Physique des Particules / CNRS, and Commissariat a l' Energie
Atomique et aux Energies Alternatives / CEA, France; the Bundesministerium f ur Bildung
und Forschung, Deutsche Forschungsgemeinschaft, and Helmholtz-Gemeinschaft Deutscher
Forschungszentren, Germany; the General Secretariat for Research and Technology, Greece;
the National Scienti c Research Foundation, and National Innovation O ce, Hungary; the
Department of Atomic Energy and the Department of Science and Technology, India; the
Institute for Studies in Theoretical Physics and Mathematics, Iran; the Science Foundation,
Ireland; the Istituto Nazionale di Fisica Nucleare, Italy; the Ministry of Science, ICT
and Future Planning, and National Research Foundation (NRF), Republic of Korea; the
Lithuanian Academy of Sciences; the Ministry of Education, and University of Malaya
(Malaysia); the Mexican Funding Agencies (BUAP, CINVESTAV, CONACYT, LNS, SEP,
and UASLP-FAI); the Ministry of Business, Innovation and Employment, New Zealand;
the Pakistan Atomic Energy Commission; the Ministry of Science and Higher Education
and the National Science Centre, Poland; the Funda c~ao para a Ci^encia e a Tecnologia,
Portugal; JINR, Dubna; the Ministry of Education and Science of the Russian Federation,
the Federal Agency of Atomic Energy of the Russian Federation, Russian Academy of
Sciences, and the Russian Foundation for Basic Research; the Ministry of Education, Science
and Technological Development of Serbia; the Secretar a de Estado de Investigaci on,
Desarrollo e Innovaci on and Programa Consolider-Ingenio 2010, Spain; the Swiss Funding
Agencies (ETH Board, ETH Zurich, PSI, SNF, UniZH, Canton Zurich, and SER); the
Ministry of Science and Technology, Taipei; the Thailand Center of Excellence in Physics,
the Institute for the Promotion of Teaching Science and Technology of Thailand, Special
Task Force for Activating Research and the National Science and Technology Development
Agency of Thailand; the Scienti c and Technical Research Council of Turkey, and Turkish Atomic Energy Authority; the National Academy of Sciences of Ukraine, and State Fund
for Fundamental Researches, Ukraine; the Science and Technology Facilities Council, UK;
the US Department of Energy, and the US National Science Foundation.
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Vardan Khachatryan, Albert M. Sirunyan, Armen Tumasyan, Wolfgang Adam1 +2356 more•Institutions (185)
TL;DR: In this paper, the production of Z bosons in pPb collisions at √SNN = 5.02 TeV is studied by the CMS experiment via the electron and muon decay channels.
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Vardan Khachatryan1, Albert M. Sirunyan1, Armen Tumasyan1, Wolfgang Adam2 +2305 more•Institutions (181)
TL;DR: Differential and integrated cross sections for the production of four leptons via the H to 4l decays (l = e, mu) are measured in pp collisions at 7 and 8 TeV.
Abstract: Differential and integrated fiducial cross sections for the production of four leptons via the H to 4l decays (l = e, mu) are measured in pp collisions at sqrt(s) = 7 and 8 TeV. Measurements are performed with data corresponding to integrated luminosities of 5.1 inverse-femtobarns at 7 TeV, and 19.7 inverse-femtobarns at 8 TeV, collected with the CMS experiment at the LHC. Differential cross sections are determined as functions of the transverse momentum and rapidity of the four-lepton system, accompanying jet multiplicity, transverse momentum of the leading jet, and difference in rapidity between the Higgs boson candidate and the leading jet. A measurement of the Z to 4l cross section, and its ratio to the H to 4l cross section is also performed. All cross sections are measured within a fiducial phase space defined by the requirements on lepton kinematics and event topology. The integrated H to 4l fiducial cross section is measured to be 0.56 +0.67-0.44 (stat) +0.21-0.06 (syst) fb at 7 TeV, and 1.11 +0.41-0.35 (stat) +0.14-0.10 (syst) fb at 8 TeV. The measurements are found to be compatible with theoretical calculations based on the standard model.
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Vardan Khachatryan1, Albert M. Sirunyan1, Armen Tumasyan1, Wolfgang Adam2 +2287 more•Institutions (181)
TL;DR: In this paper, a search for pair production of first and second generation leptoquarks is performed in final states containing either two charged leptons and two jets, or one charged lepton, one neutrino and two jet, using proton-proton collision data at √s = 8´TeV.
Abstract: A search for pair production of first and second generation leptoquarks is performed in final states containing either two charged leptons and two jets, or one charged lepton, one neutrino and two jets, using proton-proton collision data at √s = 8 TeV. The data, corresponding to an integrated luminosity of 19.7 fb^(−1), were recorded with the CMS detector at the LHC. First-generation scalar leptoquarks with masses less than 1010 (850) GeV are excluded for β=1.0 (0.5), where β is the branching fraction of a leptoquark decaying to a charged lepton and a quark. Similarly, second-generation scalar leptoquarks with masses less than 1080 (760) GeV are excluded for β=1.0 (0.5). Mass limits are also set for vector leptoquark production scenarios with anomalous vector couplings, and for R-parity violating supersymmetric scenarios of top squark pair production resulting in similar final-state signatures. These are the most stringent limits placed on the masses of vector leptoquarks and RPV top squarks to date.
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Vardan Khachatryan1, Robin Erbacher2, C. A. Carrillo Montoya3, Wagner Carvalho4 +2376 more•Institutions (180)
TL;DR: An analysis of dijet events in PbPb and pp collisions is performed to explore the properties of energy loss by partons traveling in a quark-gluon plasma as discussed by the authors.
Abstract: An analysis of dijet events in PbPb and pp collisions is performed to explore the properties of energy loss by partons traveling in a quark-gluon plasma. Data are collected at a nucleon-nucleon center-of-mass energy of 2.76 TeV at the LHC. The distribution of transverse momentum (pT) surrounding dijet systems is measured by selecting charged particles in different ranges of pT and at different angular cones of pseudorapidity and azimuth. The measurement is performed as a function of centrality of the PbPb collisions, the pT asymmetry of the jets in the dijet pair, and the distance parameter R used in the anti-kt jet clustering algorithm. In events with unbalanced dijets, PbPb collisions show an enhanced multiplicity in the hemisphere of the subleading jet, with the pT imbalance compensated by an excess of low-pT particles at large angles from the jet axes.
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Vardan Khachatryan, Albert M. Sirunyan, Armen Tumasyan, Wolfgang Adam1 +2341 more•Institutions (187)
TL;DR: In this paper, anomalous pseudoscalar couplings of the Higgs boson H to electroweak vector bosons V (=W or Z) in a sample of proton-proton collision events corresponding to an integrated luminosity of 18.9 fb^(−1) at a center-of-mass energy of 8 TeV are presented.
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Vardan Khachatryan1, Albert M. Sirunyan1, Armen Tumasyan1, Wolfgang Adam +2352 more•Institutions (188)
TL;DR: In this paper, a search for heavy Majorana neutrinos (N) decaying into a W boson and a lepton using the CMS detector at the Large Hadron Collider is performed.
Abstract: A search is performed for heavy Majorana neutrinos (N) decaying into a W boson and a lepton using the CMS detector at the Large Hadron Collider. A signature of two jets and either two same sign electrons or a same sign electron-muon pair is searched for using 19.7 inverse-femtobarns of data collected during 2012 in proton-proton collisions at a centre-of-mass energy of 8 TeV. The data are found to be consistent with the expected standard model (SM) background and, in the context of a Type-1 seesaw mechanism, upper limits are set on the cross section times branching fraction for production of heavy Majorana neutrinos in the mass range between 40 and 500 GeV. The results are additionally interpreted as limits on the mixing between the heavy Majorana neutrinos and the SM neutrinos. In the mass range considered, the upper limits range between 0.00015 - 0.72 for |V[eN]|^2 and 6.6E-5 - 0.47 for |V[eN]V*[muN]|^2 / ( |V[eN]|^2 + |V[muN]|^2 ), where V[lN] is the mixing element describing the mixing of the heavy neutrino with the SM neutrino of flavour l. These limits are the most restrictive direct limits for heavy Majorana neutrino masses above 200 GeV.
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Vardan Khachatryan1, Robin Erbacher2, C. A. Carrillo Montoya3, Wagner Carvalho4 +2297 more•Institutions (182)
TL;DR: In this article, the top quark pair production cross section is measured for the first time in proton-proton collisions at square root(s) = 13 TeV by the CMS experiment at the CERN LHC, using data corresponding to an integrated luminosity of 42 inverse picobarns.
Abstract: The top quark pair production cross section is measured for the first time in proton-proton collisions at sqrt(s) = 13 TeV by the CMS experiment at the CERN LHC, using data corresponding to an integrated luminosity of 42 inverse picobarns. The measurement is performed by analyzing events with at least one electron and one muon of opposite charge, and at least two jets. The measured cross section is 746 +/- 58 (stat) +/- 53 (syst) +/- 36 (lumi) pb, in agreement with the expectation from the standard model.
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Vardan Khachatryan1, Albert M. Sirunyan1, Armen Tumasyan1, Wolfgang Adam2 +2290 more•Institutions (182)
TL;DR: In this paper, a search is presented for the production of both first and second-generation scalar leptoquarks with a final state of either two electrons and one jet or two muons and 1 jet.
Abstract: A search is presented for the production of both first- and second-generation scalar leptoquarks with a final state of either two electrons and one jet or two muons and one jet. The search is based on a data sample of proton-proton collisions at center-of-mass energy s√=8 TeV recorded with the CMS detector and corresponding to an integrated luminosity of 19.6 fb^−1. Upper limits are set on both the first- and second-generation leptoquark production cross sections as functions of the leptoquark mass and the leptoquark couplings to a lepton and a quark. Results are compared with theoretical predictions to obtain lower limits on the leptoquark mass. At 95% confidence level, single production of first-generation leptoquarks with a coupling and branching fraction of 1.0 is excluded for masses below 1730 GeV, and second-generation leptoquarks with a coupling and branching fraction of 1.0 is excluded for masses below 530 GeV. These are the best overall limits on the production of first-generation leptoquarks to date.
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Vardan Khachatryan1, Albert M. Sirunyan1, Armen Tumasyan1, Wolfgang Adam2 +2288 more•Institutions (180)
TL;DR: In this paper, a measurement of b jet transverse momentum spectra in proton-lead (pPb) collisions using a dataset corresponding to about 35 inverse nanobarns collected with the CMS detector at the LHC is presented.
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TL;DR: In this paper, a search is presented for a new light boson with a mass of about 1 GeV and decaying promptly to jets of collimated electrons and/or muons (lepton-jets).
Abstract: A search is presented for a new, light boson with a mass of about 1 GeV and decaying promptly to jets of collimated electrons and/or muons (lepton-jets). The analysis is performed with 20.3 fb−1 of data collected by the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a centre-of-mass energy of 8 TeV. Events are required to contain at least two lepton-jets. This study finds no statistically significant deviation from predictions of the Standard Model and places 95% confidence-level upper limits on the contribution of new phenomena beyond the SM, incuding SUSY-portal and Higgs-portal models, on the number of events with lepton-jets.
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Vardan Khachatryan1, Robin Erbacher2, C. A. Carrillo Montoya3, Wagner Carvalho4 +2303 more•Institutions (176)
TL;DR: In this paper, the production cross sections of the B+, B-0, and B-s(0) mesons, and of their charge conjugates, are measured via exclusive hadronic decays in p + Pb collisions at the center-of-mass energy root s(NN) = 5.02 TeV with the CMS detector at the CERN LHC.
Abstract: The production cross sections of the B+, B-0, and B-s(0) mesons, and of their charge conjugates, are measured via exclusive hadronic decays in p + Pb collisions at the center-of-mass energy root s(NN) = 5.02 TeV with the CMS detector at the CERN LHC. The data set used for this analysis corresponds to an integrated luminosity of 34.6 nb(-1). The production cross sections are measured in the transverse momentum range between 10 and 60 GeV/c. No significant modification is observed compared to proton-proton perturbative QCD calculations scaled by the number of incoherent nucleon-nucleon collisions. These results provide a baseline for the study of in-medium b quark energy loss in Pb + Pb collisions.
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Vardan Khachatryan1, Albert M. Sirunyan1, Armen Tumasyan1, Wolfgang Adam +2283 more•Institutions (141)
TL;DR: In this article, the cross section for ttbar production in the all-jets final state is measured in pp collisions at a centre-of-mass energy of 8 TeV at the LHC with the CMS detector, in data corresponding to an integrated luminosity of 18.4 inverse femtobarns.
Abstract: The cross section for ttbar production in the all-jets final state is measured in pp collisions at a centre-of-mass energy of 8 TeV at the LHC with the CMS detector, in data corresponding to an integrated luminosity of 18.4 inverse femtobarns. The inclusive cross section is found to be 275.6 +/- 6.1 (stat) +/- 37.8 (syst) +/- 7.2 (lumi) pb. The normalized differential cross sections are measured as a function of the top quark transverse momenta, pt, and compared to predictions from quantum chromodynamics. The results are reported at detector, parton, and particle levels. In all cases, the measured top quark pt spectra are significantly softer than theoretical predictions.
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Vardan Khachatryan1, Albert M. Sirunyan1, Armen Tumasyan1, Wolfgang Adam2 +2285 more•Institutions (181)
TL;DR: In this article, a search for evidence of particle dark matter (DM) and unparticle production at the LHC has been performed using events containing two charged leptons, consistent with the decay of a Z boson, and large missing transverse momentum.
Abstract: A search for evidence of particle dark matter (DM) and unparticle production at the LHC has been performed using events containing two charged leptons, consistent with the decay of a Z boson, and large missing transverse momentum. This study is based on data collected with the CMS detector corresponding to an integrated luminosity of 19.7 inverse femtobarns of pp collisions at the LHC at a center-of-mass energy of 8 TeV. No significant excess of events is observed above the number expected from the standard model contributions. The results are interpreted in terms of 90% confidence level limits on the DM-nucleon scattering cross section, as a function of the DM particle mass, for both spin-dependent and spin-independent scenarios. Limits are set on the effective cutoff scale Lambda, and on the annihilation rate for DM particles, assuming that their branching fraction to quarks is 100%. Additionally, the most stringent 95% confidence level limits to date on the unparticle model parameters are obtained.
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Vardan Khachatryan1, Albert M. Sirunyan1, Armen Tumasyan1, Wolfgang Adam +2261 more•Institutions (142)
TL;DR: A search is presented for narrow heavy resonances X decaying into pairs of Higgs bosons in proton-proton collisions collected by the CMS experiment at the LHC at s=8TeV, significantly extending previous searches.
Abstract: A search is presented for narrow heavy resonances X decaying into pairs of Higgs bosons (H) in proton-proton collisions collected by the CMS experiment at the LHC at sqrt(s)=8 TeV. The data correspond to an integrated luminosity of 19.7 inverse femtobarns. The search considers HH resonances with masses between 1 and 3 TeV, having final states of two b quark pairs. Each Higgs boson is produced with large momentum, and the hadronization products of the pair of b quarks can usually be reconstructed as single large jets. The background from multijet and t-tbar events is significantly reduced by applying requirements related to the flavor of the jet, its mass, and its substructure. The signal would be identified as a peak on top of the dijet invariant mass spectrum of the remaining background events. No evidence is observed for such a signal. Upper limits obtained at 95% confidence level for the product of the production cross section and branching fraction sigma(gg to X) B(X to HH to b-bbar b-bbar) range from 10 to 1.5 fb for the mass of X from 1.15 to 2.0 TeV, significantly extending previous searches. For a warped extra dimension theory with a mass scale Lambda[R] = 1 TeV, the data exclude radion scalar masses between 1.15 and 1.55 TeV.