431 research outputs found

    Constraints on the Higgs boson width from off-shell production and decay to Z-boson pairs

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    Constraints are presented on the total width of the recently discovered Higgs boson, ΓH, using its relative on-shell and off-shell production and decay rates to a pair of Z bosons, where one Z boson decays to an electron or muon pair, and the other to an electron, muon, or neutrino pair. The analysis is based on the data collected by the CMS experiment at the LHC in 2011 and 2012, corresponding to integrated luminosities of 5.1fb−1at a center-of-mass energy √s=7TeVand 19.7fb−1at √s=8TeV. A simultaneous maximum likelihood fit to the measured kinematic distributions near the resonance peak and above the Z-boson pair production threshold leads to an upper limit on the Higgs boson width of ΓH\u3c22MeVat a 95% confidence level, which is 5.4 times the expected value in the standard model at the measured mass of mH=125.6GeV

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

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    Results are reported of a general search for pair production of heavy resonances decaying to pairs of hadronic jets in events with at least four jets. The study is based on up to 19.4fb−1of integrated luminosity from proton–proton collisions at a center-of-mass energy of 8TeV, recorded with the CMS detector at the LHC. Limits are determined on the production of scalar top quarks (top squarks) in the framework of R-parity violating supersymmetry and on the production of color-octet vector bosons (colorons). First limits at the LHC are placed on top squark production for two scenarios. The first assumes decay to a bottom quark and a light-flavor quark and is excluded for masses between 200 and 385GeV, and the second assumes decay to a pair of light-flavor quarks and is excluded for masses between 200 and 350GeV at 95% confidence level. Previous limits on colorons decaying to light-flavor quarks are extended to exclude masses from 200 to 835GeV

    Long-range two-particle correlations of strange hadrons with charged particles in pPb and PbPb collisions at LHC energies

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    Measurements of two-particle angular correlations between an identified strange hadron (K0Sor Λ/Λ) and a charged particle, emitted in pPb collisions, are presented over a wide range in pseudorapidity and full azimuth. The data, corresponding to an integrated luminosity of approximately 35nb−1, were collected at a nucleon–nucleon center-of-mass energy (√sNN) of 5.02TeV with the CMS detector at the LHC. The results are compared to semi-peripheral PbPb collision data at √sNN=2.76TeV, covering similar charged-particle multiplicities in the events. The observed azimuthal correlations at large relative pseudorapidity are used to extract the second-order (v2) and third-order (v3) anisotropy harmonics of K0Sand Λ/Λparticles. These quantities are studied as a function of the charged-particle multiplicity in the event and the transverse momentum of the particles. For high-multiplicity pPb events, aclear particle species dependence of v2and v3is observed. For pT\u3c2GeV, the v2and v3values of K0Sparticles are larger than those of Λ/Λparticles at the same pT. This splitting effect between two particle species is found to be stronger in pPbthan in PbPbcollisions in the same multiplicity range. When divided by the number of constituent quarks and compared at the same transverse kinetic energy per quark, both v2and v3for K0Sparticles are observed to be consistent with those for Λ/Λparticles at the 10% level in pPbcollisions. This consistency extends over a wide range of particle transverse kinetic energy and event multiplicities

    Measurement of the ttproduction cross section in pp collisions at√s=8 TeV in dilepton final states containing one τ lepton

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    The top-quark pair production cross section is measured in final states with one electron or muon and one hadronically decaying τlepton from the process tt→(ν)(τντ)bb, where =e, μ. The data sample corresponds to an integrated luminosity of 19.6fb−1collected with the CMS detector in proton–proton collisions at √s=8TeV. The measured cross section σtt=257 ±3(stat)±24(syst)±7(lumi)pb, assuming a top-quark mass of 172.5GeV, is consistent with the standard model prediction

    Search for excited quarks in the γ+jet final state in proton–proton collisions at √s=8TeV

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    A search for excited quarks decaying into the γ+jetfinal state is presented. The analysis is based on data corresponding to an integrated luminosity of 19.7fb−1collected by the CMS experiment in proton–proton collisions at √s=8TeVat the LHC. Events with photons and jets with high transverse momenta are selected and the γ+jetinvariant mass distribution is studied to search for a resonance peak. The 95% confidence level upper limits on the product of cross section and branching fraction are evaluated as a function of the excited quark mass. Limits on excited quarks are presented as a function of their mass and coupling strength; masses below 3.5TeV are excluded at 95% confidence level for unit couplings to their standard model partners

    Search for new resonances decaying via WZ to leptons in proton–proton collisions at √s=8 TeV

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    A search is performed in proton–proton collisions at √s=8TeVfor exotic particles decaying via WZ to fully leptonic final states with electrons, muons, and neutrinos. The data set corresponds to an integrated luminosity of 19.5fb−1. No significant excess is observed above the expected standard model background. Upper bounds at 95% confidence level are set on the production cross section of a Wboson as predicted by an extended gauge model, and on the WW Zcoupling. The expected and observed mass limits for a Wboson, as predicted by this model, are 1.55 and 1.47TeV, respectively. Stringent limits are also set in the context of low-scale technicolor models under a range of assumptions for the model parameters

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

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    The results of a search for new physics in final states with jets, either photons or leptons, and low missing transverse momentum are reported. The study is based on a sample of proton–proton collisions collected at a center-of-mass energy √s=8TeVwith the CMS detector in 2012. The integrated luminosity of the sample is 19.7fb−1. Many models of new physics predict the production of events with jets, electroweak gauge bosons, and little or no missing transverse momentum. Examples include stealth models of supersymmetry (SUSY), which predict a hidden sector at the electroweak energy scale in which SUSY is approximately conserved. The data are used to search for stealth SUSY signatures in final states with either two photons or an oppositely charged electron and muon. No excess is observed with respect to the standard model expectation, and the results are used to set limits on squark pair production in the stealth SUSY framework

    Inclusive search for a vector-like T quark with charge 23 in pp collisions at p s = 8 TeV

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    A search is performed for a massive new vector-like quark T, with charge 2 3 , that is pair produced together with its antiparticle in proton-proton collisions. The data were collected by the CMS experiment at the Large Hadron Collider in 2012 at p s = 8 TeV and correspond to an integrated luminosity of 19.5 fb�1. The T quark is assumed to decay into three different final states, bW, tZ, and tH. The search is carried out using events with at least one isolated lepton. No deviations from standard model expectations are observed, and lower limits are set on the T quark mass at 95% confidence level. The lower limit lies between 687 and 782 GeV for all possible values of the branching fractions into the three different final states assuming strong production. These limits are the most stringent constraints to date on the existence of such a quark

    Measurement of the cross section ratio σttbb/σttjjin ppcollisions at√s=8TeV

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    The first measurement of the cross section ratio σttbb/σttjjis presented using a data sample corresponding to an integrated luminosity of 19.6fb−1collected in pp collisions at √s=8TeVwith the CMS detector at the LHC. Events with two leptons (eor μ) and four reconstructed jets, including two identified as b quark jets, in the final state are selected. The ratio is determined for a minimum jet transverse momentum pTof both 20 and 40GeV/c. The measured ratio is 0.022 ±0.003 (stat) ±0.005 (syst)for pT\u3e20GeV/c. The absolute cross sections σttbband σttjjare also measured. The measured ratio for pT\u3e40GeV/cis compatible with a theoretical quantum chromodynamics calculation at next-to-leading order
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