M. Aguilar-Benitez

Yerevan Physics Institute, Ayrivan, Yerevan, Armenia

Are you M. Aguilar-Benitez?

Claim your profile

Publications (781)

  • Source
    [Show abstract] [Hide abstract] ABSTRACT: A search for new physics is performed based on events with jets and a pair of isolated, same-sign leptons. The results are obtained using a sample of proton-proton collision data collected by the CMS experiment at a centre-of-mass energy of 8 TeV at the LHC, corresponding to an integrated luminosity of 19.5 fb-1. In order to be sensitive to a wide variety of possible signals beyond the standard model, multiple search regions defined by the missing transverse energy, the hadronic energy, the number of jets and b-quark jets, and the transverse momenta of the leptons in the events are considered. No excess above the standard model background expectation is observed and constraints are set on a number of models for new physics, as well as on the same-sign top-quark pair and quadruple-top-quark production cross sections. Information on event selection efficiencies is also provided, so that the results can be used to confront an even broader class of new physics models. [Figure not available: see fulltext.]
    Full-text Article · Jan 2015 · Journal of High Energy Physics
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Measurements of the muon charge asymmetry in inclusive pp to WX production at sqrt(s)=7 TeV are presented. The data sample corresponds to an integrated luminosity of 4.7 inverse femtobarns recorded with the CMS detector at the LHC. With a sample of more than twenty million W to mu mu events, the statistical precision is greatly improved in comparison to previous measurements. These new results provide additional constraints on the parton distribution functions of the proton in the range of the Bjorken scaling variable x from 10E-3 to 10E-1. These measurements and the recent CMS measurement of associated W + charm production are used together with the cross sections for inclusive deep inelastic ep scattering at HERA in a next-to-leading-order QCD analysis. The determination of the valence quark distributions is improved, and the strange-quark distribution is probed directly through the leading-order process g + c to W + c in proton-proton collisions at the LHC.
    Full-text Article · Aug 2014 · Physical Review D
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Dijet production has been measured in collisions at a nucleon-nucleon centre-of-mass energy of 5.02. A data sample corresponding to an integrated luminosity of 35 was collected using the Compact Muon Solenoid detector at the Large Hadron Collider. The dijet transverse momentum balance, azimuthal angle correlations, and pseudorapidity distributions are studied as a function of the transverse energy in the forward calorimeters (). For collisions, the dijet transverse momentum ratio and the width of the distribution of dijet azimuthal angle difference are comparable to the same quantities obtained from a simulated reference and insensitive to . In contrast, the mean value of the dijet pseudorapidity is found to change monotonically with increasing , indicating a correlation between the energy emitted at large pseudorapidity and the longitudinal motion of the dijet frame. The pseudorapidity distribution of the dijet system in minimum bias collisions is compared with next-to-leading-order perturbative QCD predictions obtained from both nucleon and nuclear parton distribution functions, and the data more closely match the latter.
    Full-text Article · Jul 2014 · European Physical Journal C
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Spectra of identified charged hadrons are measured in pPb collisions with the CMS detector at the LHC at √SNN = 5.02 TeV. Charged pions, kaons, and protons in the transverse-momentum range pT ≈ 0.1-1.7GeV/c and laboratory rapidity pipeypipe < 1 are identified via their energy loss in the silicon tracker. The average pT increases with particle mass and the charged multiplicity of the event. The increase of the average pT with charged multiplicity is greater for heavier hadrons. Comparisons to Monte Carlo event generators reveal that Epos Lhc, which incorporates additional hydrodynamic evolution of the created system, is able to reproduce most of the data features, unlike Hijing and Ampt. The pT spectra and integrated yields are also compared to those measured in pp and PbPb collisions at various energies. The average transverse momentum and particle ratio measurements indicate that particle production at LHC energies is strongly correlated with event particle multiplicity. © 2014 CERN for the benefit of the CMS collaboration.
    Full-text Article · Jun 2014 · European Physical Journal C
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: A study of color coherence effects in pp collisions at a center-of-mass energy of 7TeV is presented. The data used in the analysis were collected in 2010 with the CMS detector at the LHC and correspond to an integrated luminosity of 36 pb-1. Events are selected that contain at least three jets and where the two jets with the largest transverse momentum exhibit a back-to-back topology. The measured angular correlation between the second- and third-leading jet is shown to be sensitive to color coherence effects, and is compared to the predictions of Monte Carlo models with various implementations of color coherence. None of the models describe the data satisfactorily. © 2014 The Author(s).
    Full-text Article · Jun 2014 · European Physical Journal C
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Measurements of Wγ and Zγ production in proton-proton collisions at s=7TeV are used to extract limits on anomalous triple gauge couplings. The results are based on data recorded by the CMS experiment at the LHC that correspond to an integrated luminosity of 5.0fb-1. The cross sections are measured for photon transverse momenta pTγ>15GeV, and for separations between photons and final-state charged leptons in the pseudorapidity-azimuthal plane of ΔR(,γ)>0.7 in νγ and γ final states, where refers either to an electron or a muon. A dilepton invariant mass requirement of m>50GeV is imposed for the Zγ process. No deviations are observed relative to predictions from the standard model, and limits are set on anomalous WWγ, ZZγ, and Zγγ triple gauge couplings. © 2014 CERN, for the CMS Collaboration.
    Full-text Article · May 2014 · Physical Review D
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: A search for the production of heavy partners of the top quark with charge 5/3 is performed in events with a pair of same-sign leptons. The data sample corresponds to an integrated luminosity of 19.5fb-1 and was collected at s=8TeV by the CMS experiment. No significant excess is observed in the data above the expected background, and the existence of top-quark partners with masses below 800 GeV is excluded at a 95% confidence level, assuming they decay exclusively to tW. This is the first limit on these particles from the LHC, and it is significantly more restrictive than previous limits. © 2014 CERN, for the CMS Collaboration.
    Full-text Article · Apr 2014 · Physical Review Letters
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Results are presented of a search for a "natural" supersymmetry scenario with gauge mediated symmetry breaking. It is assumed that only the supersymmetric partners of the top quark (the top squark) and the Higgs boson (Higgsino) are accessible. Events are examined in which there are two photons forming a Higgs boson candidate, and at least two b-quark jets. In 19.7fb-1 of proton-proton collision data at s=8TeV, recorded in the CMS experiment, no evidence of a signal is found and lower limits at the 95% confidence level are set, excluding the top squark mass below 360 to 410 GeV, depending on the Higgsino mass. © 2014 CERN, for the CMS Collaboration.
    Full-text Article · Apr 2014 · Physical Review Letters
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: The production of \( Y \)(1S), \( Y \)(2S), and \( Y \)(3S) is investigated in pPb and pp collisions at centre-of-mass energies per nucleon pair of 5.02 TeV and 2.76 TeV, respectively. The datasets correspond to integrated luminosities of about 31 nb−1 (pPb) and 5.4 pb−1 (pp), collected in 2013 by the CMS experiment at the LHC. Upsilons that decay into muons are reconstructed within the rapidity interval |y CM| < 1.93 in the nucleon-nucleon centre-of-mass frame. Their production is studied as a function of two measures of event activity, namely the charged-particle multiplicity measured in the pseudorapidity interval |η| < 2.4, and the sum of transverse energy deposited at forward pseudorapidity, 4.0 < |η| < 5.2. The \( Y \) cross sections normalized by their event activity integrated values, \( Y \)(nS)/〈\( Y \)(nS)〉, are found to rise with both measures of the event activity in pp and pPb. In both collision systems, the ratios of the excited to the ground state cross sections, \( Y \)(nS)/ \( Y \)(1S), are found to decrease with the charged-particle multiplicity, while as a function of the transverse energy the variation is less pronounced. The event activity integrated double ratios, [\( Y \)(nS)/ \( Y \)(1S)]pPb /[\( Y \)(nS)/ \( Y \)(1S)]pp, are also measured and found to be 0.83 ± 0.05 (stat.) ± 0.05 (syst.) and 0.71 ± 0.08 (stat.) ± 0.09 (syst.) for \( Y \)(2S) and \( Y \)(3S), respectively.
    Full-text Article · Apr 2014 · Journal of High Energy Physics
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: A search for invisible decays of Higgs bosons is performed using the vector boson fusion and associated ZH production modes. In the ZH mode, the Z boson is required to decay to a pair of charged leptons or a b b-bar quark pair. The searches use the 8 TeV pp collision dataset collected by the CMS detector at the LHC, corresponding to an integrated luminosity of up to 19.7 inverse femtobarns. Certain channels include data from 7 TeV collisions corresponding to an integrated luminosity of 4.9 inverse femtobarns. The searches are sensitive to non-standard-model invisible decays of the recently observed Higgs boson, as well as additional Higgs bosons with similar production modes and large invisible branching fractions. In all channels, the observed data are consistent with the expected standard model backgrounds. Limits are set on the production cross section times invisible branching fraction, as a function of the Higgs boson mass, for the vector boson fusion and ZH production modes. By combining all channels, and assuming standard model Higgs boson cross sections and acceptances, the observed (expected) upper limit on the invisible branching fraction at m[H]=125 GeV is found to be 0.58 (0.44) at 95% confidence level. We interpret this limit in terms of a Higgs-portal model of dark matter interactions.
    Full-text Article · Apr 2014 · European Physical Journal C
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: A search is presented for a massive particle, generically referred to as a Z', decaying into a tt̄ pair. The search focuses on Z' resonances that are sufficiently massive to produce highly Lorentz-boosted top quarks, which yield collimated decay products that are partially or fully merged into single jets. The analysis uses new methods to analyze jet substructure, providing suppression of the non-top multijet backgrounds. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 5 fb -1. Upper limits in the range of 1 pb are set on the product of the production cross section and branching fraction for a topcolor Z' modeled for several widths, as well as for a Randall-Sundrum Kaluza-Klein gluon. In addition, the result contrain any enhancement in tt̄ production beyond expectations of the standard mode for tt invariant mass larger than 1TeV/c 2.
    Full-text Article · Mar 2014 · Journal of High Energy Physics
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Results are presented from a search for the production of a heavy gauge boson W' decaying into a top and a bottom quark, using a data set collected by the CMS experiment at sqrt(s)=8 TeV and corresponding to an integrated luminosity of 19.5 inverse femtobarns. Various models of W'-boson production are studied by allowing for an arbitrary combination of left- and right-handed couplings. The analysis is based on the detection of events with a lepton (e, mu), jets, and missing transverse energy in the final state. No evidence for W'-boson production is found and 95% confidence level upper limits on the production cross section times branching fraction are obtained. For W' bosons with purely right-handed couplings, and for those with left-handed couplings assuming no interference effects, the observed 95% confidence level limit is M(W')>2.05 TeV. For W' bosons with purely left-handed couplings, including interference effects, the observed 95% confidence level limit is M(W')>1.84 TeV. The results presented in this paper are the most stringent limits published to date.
    Full-text Article · Feb 2014 · Journal of High Energy Physics
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: The production of a Z boson, decaying into two leptons and produced in association with one or more b jets, is studied using proton-proton collisions delivered by the LHC at a centre-of-mass energy of 7 TeV. The data were recorded in 2011 with the CMS detector and correspond to an integrated luminosity of 5 fb-1. The Z(ℓℓ) + b-jets cross sections (where ℓℓ = μμ or ee) are measured separately for a Z boson produced with exactly one b jet and with at least two b jets. In addition, a cross section ratio is extracted for a Z boson produced with at least one b jet, relative to a Z boson produced with at least one jet. The measured cross sections are compared to various theoretical predictions, and the data favour the predictions in the five-flavour scheme, where b quarks are assumed massless. The kinematic properties of the reconstructed particles are compared with the predictions from the MadGraph event generator using the pythia parton shower simulation. [Figure not available: see fulltext.] © 2014 The Author(s).
    Full-text Article · Feb 2014 · Journal of High Energy Physics
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: A measurement of total and fiducial inclusive W and Z boson production cross sections in pp collisions at sqrt(s)=8 TeV is presented. Electron and muon final states are analyzed in a data sample collected with the CMS detector corresponding to an integrated luminosity of 18.2 +/- 0.5 inverse picobarns. The measured total inclusive cross sections times branching fractions are sigma(pp to W X) B(W to l nu ) = 12.21 +/- 0.03 (stat.) +/- 0.24 (syst.) +/- 0.32 (lum.) nb and sigma(pp to Z X) B(Z to l+ l-) = 1.15 +/- 0.01 (stat.) +/- 0.02 (syst.) +/- 0.03 (lum.) nb for the dilepton mass in the range of 60 to 120 GeV. The measured values agree with next-to-next-to-leading-order QCD cross section calculations. Ratios of cross sections are reported with a precision of 2%. This is the first measurement of inclusive W and Z boson production in proton-proton collisions at sqrt(s)=8 TeV.
    Full-text Article · Feb 2014 · Physical Review Letters
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: A search for the standard model Higgs boson decaying to a W-boson pair at the LHC is reported. The event sample corresponds to an integrated luminosity of 4.9 fb(-1) and 19.4 fb(-1) collected with the CMS detector in pp collisions at = 7 and 8 TeV, respectively. The Higgs boson candidates are selected in events with two or three charged leptons. An excess of events above background is observed, consistent with the expectation from the standard model Higgs boson with a mass of around 125 GeV. The probability to observe an excess equal or larger than the one seen, under the background-only hypothesis, corresponds to a significance of 4.3 standard deviations for m (H) = 125.6 GeV. The observed signal cross section times the branching fraction to WW for m (H) = 125.6 GeV is times the standard model expectation. The spin-parity J (P) = 0(+) hypothesis is favored against a narrow resonance with J (P) = 2(+) or J (P) = 0(-) that decays to a W-boson pair. This result provides strong evidence for a Higgs-like boson decaying to a W-boson pair.
    Full-text Article · Jan 2014 · Journal of High Energy Physics
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: The first observation of the associated production of a single top quark and a W boson is presented. The analysis is based on a data set corresponding to an integrated luminosity of 12.2 inverse femtobarns of proton-proton collisions at sqrt(s) = 8 TeV recorded by the CMS experiment at the LHC. Events with two leptons and a jet originating from a b quark are selected. A multivariate analysis based on kinematic and topological properties is used to separate the signal from the dominant t t-bar background. An excess consistent with the signal hypothesis is observed, with a significance which corresponds to 6.1 standard deviations above a background-only hypothesis. The measured production cross section is 23.4 +/- 5.4 pb, in agreement with the standard model prediction.
    Full-text Article · Jan 2014 · Physical Review Letters
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: A search for three-jet hadronic resonance production in pp collisions at a centre-of-mass energy of 8 TeV has been conducted by the CMS Collaboration at the LHC with a data sample corresponding to an integrated luminosity of 19.4fb. The search method is model independent, and events are selected that have high jet multiplicity and large values of jet transverse momenta. The signal models explored assume R-parity-violating supersymmetric gluino pair production and have final states with either only light-flavour jets or both light- and heavy-flavour jets. No significant deviation is found between the selected events and the expected standard model multijet and tt- background. For a gluino decaying into light-flavour jets, a lower limit of 650 GeV on the gluino mass is set at a 95% confidence level, and for a gluino decaying into one heavy- and two light-flavour jets, gluino masses between 200 and 835 GeV are, for the first time, likewise excluded. © 2014 The Authors.
    Full-text Article · Jan 2014 · Physics Letters B
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: The normalised differential top quark-antiquark production cross section is measured as a function of the jet multiplicity in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC with the CMS detector. The measurement is performed in both the dilepton and lepton+jets decay channels using data corresponding to an integrated luminosity of 5.0 fb −1. Using a procedure to associate jets to decay products of the top quarks, the differential cross section of the tt production is determined as a function of the additional jet multiplicity in the lepton+jets channel. Furthermore , the fraction of events with no additional jets is measured in the dilepton channel, as a function of the threshold on the jet transverse momentum. The measurements are compared with predictions from perturbative quantum chro-modynamics and no significant deviations are observed.
    Full-text Article · Jan 2014 · European Physical Journal C
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Rapidity distributions are presented for events containing either a Z boson or a photon with a single jet in proton-proton collisions produced at the CERN LHC. The data, collected with the CMS detector at sqrt(s) = 7 TeV, correspond to an integrated luminosity of 5.0 inverse femtobarns. The individual rapidity distributions of the boson and the jet are consistent within 5% with expectations from perturbative QCD. However, QCD predictions for the sum and the difference in rapidities of the two final-state objects show discrepancies with CMS data. In particular, next-to-leading-order QCD calculations, and two common Monte Carlo event generators using different methods to match matrix-element partons with parton showers, appear inconsistent with the data as well as with each other.
    Full-text Article · Dec 2013 · Physical Review D
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: A search for flavor-changing neutral currents in top-quark decays t to Zq is performed in events produced from the decay chain t t-bar to Zq+Wb, where both vector bosons decay leptonically, producing a final state with three leptons (electrons or muons). A dataset collected with the CMS detector at the LHC is used, corresponding to an integrated luminosity of 19.7 inverse femtobarns of proton-proton collisions at a center-of-mass energy of 8 TeV. No excess is seen in the observed number of events relative to the standard model prediction; thus no evidence for flavor-changing neutral currents in top-quark decays is found. A combination with a previous search at 7 TeV excludes a t to Zq branching fraction greater than 0.05% at the 95% confidence level.
    Full-text Article · Dec 2013 · Physical Review Letters

Publication Stats

21k Citations

Institutions

  • 2010-2013
    • Yerevan Physics Institute
      Ayrivan, Yerevan, Armenia
  • 2012
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States
    • Vrije Universiteit Brussel
      • Accountancy, Auditing and Business Financing (ACCO)
      Bruxelles, Brussels Capital Region, Belgium
  • 2007
    • Complutense University of Madrid
      Madrid, Madrid, Spain
  • 1992-2007
    • University of Hamburg
      • Institut für Experimentalphysik
      Hamburg, Hamburg, Germany
  • 2006
    • Ciemat-Centro Investigaciones Energéticas, Medioambientales Y Tecnológicas
      Madrid, Madrid, Spain
  • 1984-2006
    • CERN
      Genève, Geneva, Switzerland
  • 1997-2005
    • Humboldt-Universität zu Berlin
      Berlín, Berlin, Germany
  • 2000
    • Claude Bernard University Lyon 1
      Villeurbanne, Rhône-Alpes, France
  • 1993-1997
    • University of Florence
      Florens, Tuscany, Italy
  • 1986
    • Tokyo Metropolitan University
      Edo, Tōkyō, Japan
  • 1983
    • Università degli Studi di Trieste
      Trst, Friuli Venezia Giulia, Italy
  • 1978
    • Universidad Autónoma de Madrid
      Madrid, Madrid, Spain