Measurement of the production cross section for W-bosons in association with jets in pp collisions at s=7 TeV with the ATLAS detector

This Letter reports on a first measurement of the inclusive W + jets cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC, with the ATLAS detector. Cross sections, in both the electron and muon decay modes of the W-boson, are presented as a function of jet multiplicity and of the transverse momentum of the leading and next-to-leading jets in the event. Measurements are also presented of the ratio of cross sections sigma (W + >= n)/sigma(W + >= n - 1) for inclusive jet multiplicities n = 1-4. The results, based on an integrated luminosity of 1.3 pb(-1), have been corrected for all known detector effects and are quoted in a limited and well-defined range of jet and lepton kinematics. The measured cross sections are compared to particle-level predictions based on perturbative QCD. Next-to-leading order calculations, studied here for n <= 2, are found in good agreement with the data. Leading-order multiparton event generators, normalized to the NNLO total cross section, describe the data well for all measured jet multiplicitie

Observation of the diphoton decay of the Higgs boson and measurement of its properties

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Study of Vector Boson Scattering and Search for New Physics in Events with Two Same-Sign Leptons and Two Jets

A study of vector boson scattering in pp collisions at a center-of-mass energy of 8 TeV is presented. The data sample corresponds to an integrated luminosity of 19.4 fb(-1) collected with the CMS detector. Candidate events are selected with exactly two leptons of the same charge, two jets with large rapidity separation and high dijet mass, and moderate missing transverse energy. The signal region is expected to be dominated by electroweak same-sign W-boson pair production. The observation agrees with the standard model prediction. The observed significance is 2.0 standard deviations, where a significance of 3.1 standard deviations is expected based on the standard model. Cross section measurements for (WW +/-)-W-+/- and WZ processes in the fiducial region are reported. Bounds on the structure of quartic vector-boson interactions are given in the framework of dimension-eight effective field theory operators, as well as limits on the production of doubly charged Higgs bosons

Search for a W or Techni-rho Decaying into WZ in pp Collisions at root s=7 TeV

A search is performed in pp collisions at root 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

Search for a light charged Higgs boson decaying to c-sbar in pp collisions at sqrt(s) = 8 TeV

see paper for full list of authorsInternational audienceA search for a light charged Higgs boson, originating from the decay of a top quark and subsequently decaying into a charm quark and a strange antiquark, is presented. The data used in the analysis correspond to an integrated luminosity of 19.7 inverse-femtobarns recorded in proton-proton collisions at sqrt(s) = 8 TeV by the CMS experiment at the LHC. The search is performed in the process t tbar to W+/- b H-/+ bbar, where the W boson decays to a lepton (electron or muon) and a neutrino. The decays lead to a final state comprising an isolated lepton, at least four jets and large missing transverse energy. No significant deviation is observed in the data with respect to the standard model predictions, and model-independent upper limits are set on the branching fraction BF( t to H+ b ), ranging from 1.2 to 6.5% for a charged Higgs boson with mass between 90 and 160 GeV, under the assumption that BF( H+ to c sbar ) = 100%

Measurement of transverse momentum relative to dijet systems in PbPb and pp collisions at sqrt(s) = 8 TeV

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

Search for heavy neutrinos and W bosons with right-handed couplings in proton-proton collisions at sqrt(s) = 8 TeV

Submitted to Eur. Phys. J. C. arXiv admin note: text overlap with arXiv:1405.7225 ; see paper for full list of authorsA search for heavy, right-handed neutrinos, N[l] (l = e, mu), and right-handed WR bosons, which arise in the left-right symmetric extensions of the standard model, has been performed by the CMS experiment. The search was based on a sample of two lepton plus two jet events collected in proton-proton collisions at a center-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.7 inverse femtobarns. No significant excess of events over the standard model expectation is observed. For models with strict left-right symmetry, and assuming only one N[l] flavor contributes significantly to the WR decay width, the region in the two-dimensional (M[WR], M[N]) mass plane excluded at a 95% confidence level extends to approximately M[WR] = 3.0 TeV and covers a large range of neutrino masses below the WR boson mass, depending on the value of M[WR]. This search significantly extends the (M[WR], M[N]) exclusion region beyond previous results

Measurement of the ratio B(t›Wb)/B(t›Wq) in pp collisions at s=8 TeV

The ratio of the top-quark branching fractions R=B(t›Wb)/B(t›Wq), where the denominator includes the sum over all down-type quarks (q=b,s,d), is measured in the tt¯ dilepton final state with proton–proton collision data at s=8 TeV from an integrated luminosity of 19.7 fb-1, collected with the CMS detector. In order to quantify the purity of the signal sample, the cross section is measured by fitting the observed jet multiplicity, thereby constraining the signal and background contributions. By counting the number of b jets per event, an unconstrained value of R=1.014±0.003(stat.)±0.032(syst.) is measured, in a good agreement with current precision measurements in electroweak and flavour sectors. A lower limit R&gt;0.955 at the 95% confidence level is obtained after requiring R?1, and a lower limit on the Cabibbo–Kobayashi–Maskawa matrix element |Vtb|&gt;0.975 is set at 95% confidence level. The result is combined with a previous CMS measurement of the t-channel single-top-quark cross section to determine the top-quark total decay width, ?t=1.36±0.02(stat.)-0.11 +0.14(syst.) GeV. © 2014 The Author

Search for supersymmetry in hadronic final states with missing transverse energy using the variables αT and b-quark multiplicity in pp collisions at √s = 8 TeV

Submitted by Vitor Silverio Rodrigues ([email protected]) on 2014-05-27T11:30:34Z No. of bitstreams: 0Bitstream added on 2014-05-27T14:48:49Z : No. of bitstreams: 1 2-s2.0-84883824987.pdf: 1540579 bytes, checksum: be6bbff5192436d9fcdbc367ffd1650e (MD5) Made available in DSpace on 2014-05-27T11:30:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-09-01 An inclusive search for supersymmetric processes that produce final states with jets and missing transverse energy is performed in pp collisions at a centre-of-mass energy of 8 TeV. The data sample corresponds to an integrated luminosity of 11.7 fb-1 collected by the CMS experiment at the LHC. In this search, a dimensionless kinematic variable, αT, is used to discriminate between events with genuine and misreconstructed missing transverse energy. The search is based on an examination of the number of reconstructed jets per event, the scalar sum of transverse energies of these jets, and the number of these jets identified as originating from bottom quarks. No significant excess of events over the standard model expectation is found. Exclusion limits are set in the parameter space of simplified models, with a special emphasis on both compressed-spectrum scenarios and direct or gluino-induced production of third-generation squarks. For the case of gluino-mediated squark production, gluino masses up to 950-1125 GeV are excluded depending on the assumed model. For the direct pair-production of squarks, masses up to 450 GeV are excluded for a single light first- or second-generation squark, increasing to 600 GeV for bottom squarks. © 2013 CERN for the benefit of the CMS collaboration. CERN, Geneva Yerevan Physics Institute, Yerevan Institut für Hochenergiephysik der OeAW, Wien National Centre for Particle and High Energy Physics, Minsk Universiteit Antwerpen, Antwerpen Vrije Universiteit Brussel, Brussel Université Libre de Bruxelles, Bruxelles Ghent University, Ghent Université Catholique de Louvain, Louvain-la-Neuve Université de Mons, Mons Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro Universidade do Estado do Rio de Janeiro, Rio de Janeiro Universidade Estadual Paulista, São Paulo Universidade Federal do ABC, São Paulo Institute for Nuclear Research and Nuclear Energy, Sofia University of Sofia, Sofia Institute of High Energy Physics, Beijing State Key Laboratory of Nuclear Physics and Technology Peking University, Beijing Universidad de Los Andes, Bogota Technical University of Split, Split University of Split, Split Institute Rudjer Boskovic, Zagreb University of Cyprus, Nicosia Charles University, Prague Academy of Scientific Research and Technology of the Arab Republic of Egypt Egyptian Network of High Energy Physics, Cairo National Institute of Chemical Physics and Biophysics, Tallinn Department of Physics University of Helsinki, Helsinki Helsinki Institute of Physics, Helsinki Lappeenranta University of Technology, Lappeenranta DSM/IRFU CEA/Saclay, Gif-sur-Yvette Laboratoire Leprince-Ringuet, Ecole Polytechnique IN2P3-CNRS, Palaiseau Institut Pluridisciplinaire Hubert Curien, Universite de Strasbourg, Universite de Haute Alsace Mulh CNRS/IN2P3, Strasbourg CNRS-IN2P3, Institut de Physique Nucléaire de Lyon Université de Lyon, Université Claude Bernard Lyon 1, Villeurbanne Institute of High Energy Physics and Informatization Tbilisi State University, Tbilisi I. Physikalisches Institut RWTH Aachen University, Aachen III. Physikalisches Institut A RWTH Aachen University, Aachen III. 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