Publications (88)508.37 Total impact
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Article: Study of the Mass and Spin-Parity of the Higgs Boson Candidate via Its Decays to Z Boson Pairs.
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ABSTRACT: A study is presented of the mass and spin-parity of the new boson recently observed at the LHC at a mass near 125 GeV. An integrated luminosity of 17.3 fb^{-1}, collected by the CMS experiment in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, is used. The measured mass in the ZZ channel, where both Z bosons decay to e or μ pairs, is 126.2±0.6(stat)±0.2(syst) GeV. The angular distributions of the lepton pairs in this channel are sensitive to the spin-parity of the boson. Under the assumption of spin 0, the present data are consistent with the pure scalar hypothesis, while disfavoring the pure pseudoscalar hypothesis.Physical Review Letters 02/2013; 110(8):081803. · 7.37 Impact Factor -
Article: Search for Pair Production of Third-Generation Leptoquarks and Top Squarks in pp Collisions at sqrt[s]=7 TeV.
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ABSTRACT: Results are presented from a search for the pair production of third-generation scalar and vector leptoquarks, as well as for top squarks in R-parity-violating supersymmetric models. In either scenario, the new, heavy particle decays into a τ lepton and a b quark. The search is based on a data sample of pp collisions at sqrt[s]=7 TeV, which is collected by the CMS detector at the LHC and corresponds to an integrated luminosity of 4.8 fb^{-1}. The number of observed events is found to be in agreement with the standard model prediction, and exclusion limits on mass parameters are obtained at the 95% confidence level. Vector leptoquarks with masses below 760 GeV are excluded and, if the branching fraction of the scalar leptoquark decay to a τ lepton and a b quark is assumed to be unity, third-generation scalar leptoquarks with masses below 525 GeV are ruled out. Top squarks with masses below 453 GeV are excluded for a typical benchmark scenario, and limits on the coupling between the top squark, τ lepton, and b quark, λ_{333}^{'} are obtained. These results are the most stringent for these scenarios to date.Physical Review Letters 02/2013; 110(8):081801. · 7.37 Impact Factor -
Article: Measurement of the Υ(1S), Υ(2S), and Υ(3S) Polarizations in pp Collisions at sqrt[s]=7 TeV.
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ABSTRACT: The polarizations of the Υ(1S), Υ(2S), and Υ(3S) mesons are measured in proton-proton collisions at sqrt[s]=7 TeV, using a data sample of Υ(nS)→μ^{+}μ^{-} decays collected by the CMS experiment, corresponding to an integrated luminosity of 4.9 fb^{-1}. The dimuon decay angular distributions are analyzed in three different polarization frames. The polarization parameters λ_{ϑ}, λ_{φ}, and λ_{ϑφ}, as well as the frame-invariant quantity λ[over ˜], are presented as a function of the Υ(nS) transverse momentum between 10 and 50 GeV, in the rapidity ranges |y|<0.6 and 0.6<|y|<1.2. No evidence of large transverse or longitudinal polarizations is seen in the explored kinematic region.Physical Review Letters 02/2013; 110(8):081802. · 7.37 Impact Factor -
Article: Evidence for Associated Production of a Single Top Quark and W Boson in pp Collisions at sqrt[s]=7 TeV.
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ABSTRACT: Evidence is presented for the associated production of a single top quark and W boson in pp collisions at sqrt[s]=7 TeV with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 4.9 fb^{-1}. The measurement is performed using events with two leptons and a jet originated from a b quark. A multivariate analysis based on kinematic properties is utilized to separate the tt[over ¯] background from the signal. The observed signal has a significance of 4.0σ and corresponds to a cross section of 16_{-4}^{+5} pb, in agreement with the standard model expectation of 15.6±0.4_{-1.2}^{+1.0} pb.Physical Review Letters 01/2013; 110(2):022003. · 7.37 Impact Factor -
Article: Search for Heavy Neutrinos and W_{R} Bosons with Right-Handed Couplings in a Left-Right Symmetric Model in pp Collisions at sqrt[s]=7 TeV.
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ABSTRACT: Results are presented from a search for heavy, right-handed muon neutrinos, N_{μ}, and right-handed W_{R} bosons, which arise in the left-right symmetric extensions of the standard model. The analysis is based on a 5.0 fb^{-1} sample of proton-proton collisions at a center-of-mass energy of 7 TeV, collected by the CMS detector at the Large Hadron Collider. No evidence is observed for an excess of events over the standard model expectation. For models with exact left-right symmetry, heavy right-handed neutrinos are excluded at 95% confidence level for a range of neutrino masses below the W_{R} mass, dependent on the value of M_{W_{R}}. The excluded region in the two-dimensional (M_{W_{R}}, M_{N_{μ}}) mass plane extends to M_{W_{R}}=2.5 TeV.Physical Review Letters 12/2012; 109(26):261802. · 7.37 Impact Factor -
Article: Study of the Dijet Mass Spectrum in pp→W+jets Events at sqrt[s]=7 TeV.
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ABSTRACT: We report an investigation of the invariant mass spectrum of the two jets with highest transverse momentum in pp→W+2-jet and W+3-jet events to look for resonant enhancement. The data sample corresponds to an integrated luminosity of 5.0 fb^{-1} collected with the CMS detector at sqrt[s]=7 TeV. We find no evidence for the anomalous structure reported by the CDF Collaboration, and establish an upper limit of 5.0 pb at 95% confidence level on the production cross section for a generic Gaussian signal with mass near 150 GeV. Additionally, we exclude two theoretical models that predict a CDF-like dijet resonance near 150 GeV.Physical Review Letters 12/2012; 109(25):251801. · 7.37 Impact Factor -
Article: A New Boson with a Mass of 125 GeV Observed with the CMS Experiment at the Large Hadron Collider
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ABSTRACT: The Higgs boson was postulated nearly five decades ago within the framework of the standard model of particle physics and has been the subject of numerous searches at accelerators around the world. Its discovery would verify the existence of a complex scalar field thought to give mass to three of the carriers of the electroweak force—the W+, W–, and Z0 bosons—as well as to the fundamental quarks and leptons. The CMS Collaboration has observed, with a statistical significance of five standard deviations, a new particle produced in proton-proton collisions at the Large Hadron Collider at CERN. The evidence is strongest in the diphoton and four-lepton (electrons and/or muons) final states, which provide the best mass resolution in the CMS detector. The probability of the observed signal being due to a random fluctuation of the background is about 1 in 3 × 106. The new particle is a boson with spin not equal to 1 and has a mass of about 1.25 giga–electron volts. Although its measured properties are, within the uncertainties of the present data, consistent with those expected of the Higgs boson, more data are needed to elucidate the precise nature of the new particle.Science 12/2012; 338(6114):1569-1575. · 31.20 Impact Factor -
Article: Observation of Sequential Υ Suppression in PbPb Collisions.
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ABSTRACT: The suppression of the individual Υ(nS) states in PbPb collisions with respect to their yields in pp data has been measured. The PbPb and pp data sets used in the analysis correspond to integrated luminosities of 150 μb^{-1} and 230 nb^{-1}, respectively, collected in 2011 by the CMS experiment at the LHC, at a center-of-mass energy per nucleon pair of 2.76 TeV. The Υ(nS) yields are measured from the dimuon invariant mass spectra. The suppression of the Υ(nS) yields in PbPb relative to the yields in pp, scaled by the number of nucleon-nucleon collisions, R_{AA}, is measured as a function of the collision centrality. Integrated over centrality, the R_{AA} values are 0.56±0.08(stat)±0.07(syst), 0.12±0.04(stat)±0.02(syst), and lower than 0.10 (at 95% confidence level), for the Υ(1S), Υ(2S), and Υ(3S) states, respectively. The results demonstrate the sequential suppression of the Υ(nS) states in PbPb collisions at LHC energies.Physical Review Letters 11/2012; 109(22):222301. · 7.37 Impact Factor -
Article: Search for New Physics in the Multijet and Missing Transverse Momentum Final State in Proton-Proton Collisions at sqrt[s]=7 TeV.
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ABSTRACT: A search for physics beyond the standard model is performed in events with at least three jets and large missing transverse momentum produced in proton-proton collisions at a center-of-mass energy of sqrt[s]=7 TeV. No significant excess of events above the expected backgrounds is observed in 4.98 fb^{-1} of data collected with the CMS detector at the Large Hadron Collider. The results are presented in the context of the constrained minimal supersymmetric extension of the standard model and more generically for simplified models. For the simplified models of gluino-gluino and squark-squark production, gluino masses below 1.0 TeV and squark masses below 0.76 TeV are excluded in case the lightest supersymmetric particle mass is below 200 GeV. These results significantly extend previous searches.Physical Review Letters 10/2012; 109(17):171803. · 7.37 Impact Factor -
Article: Measurement of the Pseudorapidity and Centrality Dependence of the Transverse Energy Density in Pb-Pb Collisions at sqrt[s_{NN}]=2.76 TeV.
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ABSTRACT: The transverse energy (E_{T}) in Pb-Pb collisions at 2.76 TeV nucleon-nucleon center-of-mass energy (sqrt[s_{NN}]) has been measured over a broad range of pseudorapidity (η) and collision centrality by using the CMS detector at the LHC. The transverse energy density per unit pseudorapidity (dE_{T}/dη) increases faster with collision energy than the charged particle multiplicity. This implies that the mean energy per particle is increasing with collision energy. At all pseudorapidities, the transverse energy per participating nucleon increases with the centrality of the collision. The ratio of transverse energy per unit pseudorapidity in peripheral to central collisions varies significantly as the pseudorapidity increases from η=0 to |η|=5.0. For the 5% most central collisions, the energy density per unit volume is estimated to be about 14 GeV/fm^{3} at a time of 1 fm/c after the collision. This is about 100 times larger than normal nuclear matter density and a factor of 2.6 times higher than the energy density reported at sqrt[s_{NN}]=200 GeV at the Relativistic Heavy Ion Collider.Physical Review Letters 10/2012; 109(15):152303. · 7.37 Impact Factor -
Article: Search for a W^{'} or Techni-ρ Decaying into WZ in pp Collisions at sqrt[s]=7 TeV.
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ABSTRACT: A search is performed in pp collisions at sqrt[s]=7 TeV for exotic particles decaying via WZ to final states with electrons and muons. The data sample corresponds to an integrated luminosity of approximately 5 fb^{-1}. No significant excess is observed in the data above the expected standard model background. Upper bounds at 95% confidence level are set on the production cross section of the W^{'} boson described by the sequential standard model and on the W^{'} WZ coupling. W^{'} bosons with masses below 1143 GeV are excluded. Limits are also set in the context of low-scale technicolor models, under a range of assumptions concerning the model parameters.Physical Review Letters 10/2012; 109(14):141801. · 7.37 Impact Factor -
Article: Search for a Light Pseudoscalar Higgs Boson in the Dimuon Decay Channel in pp Collisions at sqrt[s]=7 TeV.
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ABSTRACT: The dimuon invariant mass spectrum is searched in the range between 5.5 and 14 GeV for a light pseudoscalar Higgs boson a, predicted in a number of new physics models, including the next-to-minimal supersymmetric standard model. The data sample used in the search corresponds to an integrated luminosity of 1.3 fb^{-1} collected in pp collisions at sqrt[s]=7 TeV with the CMS detector at the LHC. No excess is observed above the background predictions and upper limits are set on the cross section times branching fraction σ×B(pp→a→μ^{+}μ^{-}) in the range of 1.5-7.5 pb. These results improve on existing bounds on the abb[over ¯] coupling for m_{a}<m_{Υ(1S)} and are the first significant limits for m_{a}>m_{Υ(3S)}. Constraints on the supersymmetric parameter space are presented in the context of the next-to-minimal model.Physical Review Letters 09/2012; 109(12):121801. · 7.37 Impact Factor -
Article: Azimuthal Anisotropy of Charged Particles at High Transverse Momenta in Pb-Pb Collisions at sqrt[s_{NN}]=2.76 TeV.
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ABSTRACT: The azimuthal anisotropy of charged particles in Pb-Pb collisions at sqrt[s_{NN}]=2.76 TeV is measured with the CMS detector at the LHC over an extended transverse momentum (p_{T}) range up to approximately 60 GeV/c. The data cover both the low-p_{T} region associated with hydrodynamic flow phenomena and the high-p_{T} region where the anisotropies may reflect the path-length dependence of parton energy loss in the created medium. The anisotropy parameter (v_{2}) of the particles is extracted by correlating charged tracks with respect to the event-plane reconstructed by using the energy deposited in forward-angle calorimeters. For the six bins of collision centrality studied, spanning the range of 0-60% most-central events, the observed v_{2} values are found to first increase with p_{T}, reaching a maximum around p_{T}=3 GeV/c, and then to gradually decrease to almost zero, with the decline persisting up to at least p_{T}=40 GeV/c over the full centrality range measured.Physical Review Letters 07/2012; 109(2):022301. · 7.37 Impact Factor -
Article: Search for neutral Higgs bosons decaying to tau pairs in pp collisions at s=7 TeV
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ABSTRACT: A search for neutral Higgs bosons decaying to tau pairs at a center-of-mass energy of 7 TeV is performed using a dataset corresponding to an integrated luminosity of 4.6 fb-1 recorded by the CMS experiment at the LHC. The search is sensitive to both the standard model Higgs boson and to the neutral Higgs bosons predicted by the minimal supersymmetric extension of the standard model (MSSM). No excess of events is observed in the tau-pair invariant-mass spectrum. For a standard model Higgs boson in the mass range of 110-145 GeV upper limits at 95% confidence level (CL) on the production cross section are determined. We exclude a Higgs boson with mH=115 GeV with a production cross section 3.2 times of that predicted by the standard model. In the MSSM, upper limits on the neutral Higgs boson production cross section times branching fraction to tau pairs, as a function of the pseudoscalar Higgs boson mass, mA, sets stringent new bounds in the parameter space, excluding at 95% CL values of tan β as low as 7.1 at mA=160 GeV in the mhmax benchmark scenario.Physics Letters B 05/2012; 713:68-90. · 3.95 Impact Factor -
Article: Measurement of the production cross section in pp collisions at TeV using the kinematic properties of events with leptons and jets
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ABSTRACT: A measurement of the t[`(t)]\mathrm{t{\bar{t}}} production cross section in proton-proton collisions at a centre-of-mass energy of 7TeV has been performed at the LHC with the CMS detector. The analysis uses a data sample corresponding to an integrated luminosity of 36pb−1 and is based on the reconstruction of the final state with one isolated, high transverse-momentum electron or muon and three or more hadronic jets. The kinematic properties of the events are used to separate the t[`(t)]\mathrm{t{\bar{t}}} signal from W+jets and QCD multijet background events. The measured cross section is 173+39-32(stat. + syst.)173^{+39}_{-32}~(\mathrm{stat}. + \mathrm{syst}.)pb, consistent with standard model expectations.European Physical Journal C 05/2012; 71(9):1-27. · 3.63 Impact Factor -
Article: Search for new physics with jets and missing transverse momentum in pp collisions at TeV
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ABSTRACT: A search for new physics is presented based on an event signature of at least three jets accompanied by large missing transverse momentum, using a data sample corresponding to an integrated luminosity of 36 pb−1 collected in proton-proton collisions at Ös = 7 \sqrt {s} = 7 TeV with the CMS detector at the LHC. No excess of events is observed above the expected standard model backgrounds, which are all estimated from the data. Exclusion limits are presented for the constrained minimal supersymmetric extension of the standard model. Cross section limits are also presented using simplified models with new particles decaying to an undetected particle and one or two jets. KeywordsHadron-Hadron ScatteringJournal of High Energy Physics 04/2012; 2011(8):1-46. · 5.83 Impact Factor -
Article: Measurement of the inclusive Z cross section via decays to tau pairs in pp collisions at TeV
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ABSTRACT: The first measurement of inclusive Z → τ + τ − production in pp collisions at the LHC is presented, in the final states μ + hadrons, e + hadrons, e + μ, and μ + μ. The data sample corresponds to an integrated luminosity of 36 pb−1 collected with the CMS detector. The measured cross section is σ (pp → ZX) × B (Z → τ + τ −) = 1.00 ± 0.05(stat.) ± 0.08(syst.) ± 0.04(lumi.)nb, which is in good agreement with the next-to-next-to-leading order QCD prediction and improves on previous measurements in the Z → e+e− and μ + μ − channels. The reconstruction efficiency for hadronic τ decays is determined with a precision of 7%. KeywordsHadron-Hadron ScatteringJournal of High Energy Physics 04/2012; 2011(8):1-32. · 5.83 Impact Factor -
Article: Measurement of the underlying event activity at the LHC with TeV and comparison with TeV
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ABSTRACT: A measurement of the underlying activity in events with a jet of transverse momentum in the several GeV region is performed in proton-proton collisions at Ös = 0.9 \sqrt {s} = 0.9 and 7 TeV, using data collected by the CMS experiment at the LHC. The production of charged particles with pseudorapidity |η| < 2 and transverse momentum p T > 0.5GeV/c is studied in the azimuthal region transverse to that of the leading set of charged particles forming a track-jet. A significant growth of the average multiplicity and scalar-p T sum of the particles in the transverse region is observed with increasing p T of the leading track-jet, followed by a much slower rise above a few GeV/c. For track-jet p T larger than a few GeV/c, the activity in the transverse region is approximately doubled with a centre-of-mass energy increase from 0.9 to 7 TeV. Predictions of several QCD-inspired models as implemented in pythia are compared to the data. KeywordsHadron-Hadron ScatteringJournal of High Energy Physics 04/2012; 2011(9):1-31. · 5.83 Impact Factor -
Article: Search for supersymmetry in events with a lepton, a photon, and large missing transverse energy in pp collisions at TeV
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ABSTRACT: A search is performed for an excess of events, over the standard model expectations, with a photon, a lepton, and large missing transverse energy in pp collisions at Ös = 7 \sqrt {s} = 7 TeV. Such events are expected in many new physics models, in particular a supersymmetric theory that is broken via a gauge-mediated mechanism, when the lightest charged and neutral gauginos are mass degenerate. The data sample used in this search corresponds to an integrated luminosity of 35 pb-1 collected with the CMS detector at the LHC. No evidence of such an excess above the standard model backgrounds, dominated by W production, is found. The results are presented as 95% confidence level upper limits on the cross section for a benchmark gauge-mediated scenario, and are then converted into exclusion limits on the squark, gluino, and wino masses. KeywordsHadron-Hadron ScatteringJournal of High Energy Physics 04/2012; 2011(6):1-28. · 5.83 Impact Factor -
Article: Search for resonances in the dilepton mass distribution in pp collisions at TeV
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ABSTRACT: A search for narrow resonances at high mass in the dimuon and dielectron channels has been performed by the CMS experiment at the CERN LHC, using pp collision data recorded at Ös = 7 \sqrt {s} = 7 TeV. The event samples correspond to integrated luminosities of 40 pb−1 in the dimuon channel and 35 pb−1 in the dielectron channel. Heavy dilepton resonances are predicted in theoretical models with extra gauge bosons (Z′) or as Kaluza-Klein graviton excitations (GKK) in the Randall-Sundrum model. Upper limits on the inclusive cross section of Z′(GKK) → ℓ + ℓ − relative to Z → ℓ + ℓ − are presented. These limits exclude at 95% confidence level a Z′ with standard-model-like couplings below 1140GeV, the superstring-inspired Z ψ ′ below 887 GeV, and, for values of the coupling parameter k / [`(M)] \textPl {{k} \left/ {{{{\overline M }_{\text{Pl}}}}} \right.} of 0.05 (0.1), Kaluza-Klein gravitons below 855 (1079) GeV. KeywordsHadron-Hadron ScatteringJournal of High Energy Physics 04/2012; 2011(5):1-35. · 5.83 Impact Factor
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2010–2013
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Yerevan Physics Institute
Yerevan, K'aghak' Yerevan, Armenia
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