Results are reported from a search for the production of three-jet resonances in pp collisions at a center-of-mass energy s = 7 TeV . The study uses the data sample collected by the CMS experiment at ...the LHC in 2011, corresponding to an integrated luminosity of 5.0 fb - 1 . Events with high jet multiplicity and a large scalar sum of jet transverse momenta are analyzed for the presence of resonances in the three-jet invariant mass spectrum. No evidence for a narrow resonance is found in the data, and limits are set on the cross section for gluino pair production in an R-parity-violating supersymmetry model, for gluino masses greater than 280 GeV. Assuming a branching fraction for gluino decay into three jets of 100%, gluino masses below 460 GeV are excluded at 95% confidence level. These results significantly extend the range of previous limits.
A search is presented for physics beyond the standard model (BSM) in final states with a pair of opposite-sign isolated leptons accompanied by jets and missing transverse energy. The search uses LHC ...data recorded at a center-of-mass energy s = 7 TeV with the CMS detector, corresponding to an integrated luminosity of approximately 5 fb-1. Two complementary search strategies are employed. The first probes models with a specific dilepton production mechanism that leads to a characteristic kinematic edge in the dilepton mass distribution. The second strategy probes models of dilepton production with heavy, colored objects that decay to final states including invisible particles, leading to very large hadronic activity and missing transverse energy. No evidence for an event yield in excess of the standard model expectations is found. Upper limits on the BSM contributions to the signal regions are deduced from the results, which are used to exclude a region of the parameter space of the constrained minimal supersymmetric extension of the standard model. Additional information related to detector efficiencies and response is provided to allow testing specific models of BSM physics not considered in this Letter.
A measurement of the forward-backward asymmetry (A FB) of Drell-Yan lepton pairs in pp collisions at s = 7 TeV is presented. The data sample, collected with the CMS detector, corresponds to an ...integrated luminosity of 5 fb - 1 . The asymmetry is measured as a function of dilepton mass and rapidity in the dielectron and dimuon channels. Combined results from the two channels are presented, and are compared with the standard model predictions. The A FB measurement in the dimuon channel and the combination of the two channels are the first such results obtained at a hadron collider. The measured asymmetries are consistent with the standard model predictions.
Results from the first study of isolated-photon + jet correlations in relativistic heavy ion collisions are reported. The analysis uses data from PbPb collisions at a centre-of-mass energy of 2.76 ...TeV per nucleon pair corresponding to an integrated luminosity of 150 mu b - 1 recorded by the CMS experiment at the LHC. For events containing an isolated photon with transverse momentum p T gamma > 60 GeV / c and an associated jet with p T Jet > 30 GeV / c , the photon + jet p T imbalance is studied as a function of collision centrality and compared to pp data and pythia calculations at the same collision energy. Using the p T gamma of the isolated photon as an estimate of the momentum of the associated parton at production, this measurement allows an unbiased characterisation of the in-medium parton energy loss. For more central PbPb collisions, a significant decrease in the ratio p T Jet / p T gamma relative to that in the pythia reference is observed. Furthermore, significantly more p T gamma > 60 GeV / c photons in PbPb are observed not to have an associated p T Jet > 30 GeV / c jet, compared to the reference. However, no significant broadening of the photon + jet azimuthal correlation is observed.
A search is presented for charge-asymmetric production of a W ' boson that has been proposed to accommodate the forward-backward asymmetry observed in the production of top-antitop quark pairs at the ...Tevatron. The new heavy W ' boson would be produced in association with a top quark and would decay into top and down quarks. The data correspond to an integrated luminosity of 5.0 fb-1 in pp collisions at a center-of-mass energy of 7 TeV, recorded by the CMS detector at the LHC. No significant excess above the standard model expectations is observed, and, from a combination of the electron-plus-jets and muon-plus-jets channels, a 95% confidence level lower limit of 840 GeV / c 2 is set on the W ' boson mass for a W ' boson model with values for coupling constants to top and down quarks g L = 0 and g R = 2 . In addition, a kinematic reconstruction of the W ' resonance mass using the inherent charge asymmetry of this model finds no indication of the presence of W ' events in the data.
A search is presented for physics beyond the standard model (BSM) in events with a Z boson, jets, and missing transverse energy (E T miss). This signature is motivated by BSM physics scenarios, ...including supersymmetry. The study is performed using a sample of proton-proton collision data collected at s = 7 TeV with the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.98 fb-1. The contributions from the dominant standard model backgrounds are estimated from data using two complementary strategies, the jet-Z balance technique and a method based on modeling E T miss with data control samples. In the absence of evidence for BSM physics, we set limits on the non-standard-model contributions to event yields in the signal regions and interpret the results in the context of simplified model spectra. Additional information is provided to facilitate tests of other BSM physics models.
The results of a search for pair production of a heavy, top-like quark, t ' , in the decay mode t ' t A= ' ? bW + b A= W - ? b l + ? b A= l - ? A= are presented. The search is performed with a data ...sample corresponding to an integrated luminosity of 5.0 fb - 1 in pp collisions at a center-of-mass energy of 7 TeV, collected by the CMS experiment at the LHC. The observed number of events agrees with the expectation from standard model processes, and no evidence of t ' t A= ' production is found. Upper limits on the production cross section as a function of t ' mass are presented, and t ' masses below 557 GeV / c 2 are excluded at the 95% confidence level.
A search for high-mass resonances decaying into t + t - is performed using a data sample of pp collisions at s = 7 TeV . The data were collected with the CMS detector at the LHC and correspond to an ...integrated luminosity of 4.9 fb-1. The number of observed events is in agreement with the standard model prediction. An upper limit on the product of the resonance cross section and branching fraction into t-lepton pairs is calculated as a function of the resonance mass. Using the sequential standard model resonance Z SSM ' and the superstring-inspired E 6 model with resonance Z ? ' as benchmarks, resonances with standard model couplings with masses below 1.4 and 1.1 TeV, respectively, are excluded at 95% confidence level.
A measurement is presented of W-boson production in PbPb collisions carried out at a nucleon-nucleon (NN) centre-of-mass energy s NN of 2.76 TeV at the LHC using the CMS detector. In data ...corresponding to an integrated luminosity of 7.3 mu b - 1 , the number of W ? mu ? mu decays is extracted in the region of muon pseudorapidity | ? mu | 25 GeV / c . Yields of muons found per unit of pseudorapidity correspond to (159 +/- 10 (stat.) +/- 12 (syst.)) X 10 - 8 W + and (154 +/- 10 (stat.) +/- 12 (syst.)) X 10 - 8 W - bosons per minimum-bias PbPb collision. The dependence of W production on the centrality of PbPb collisions is consistent with a scaling of the yield by the number of incoherent NN collisions. The yield of W bosons is also studied in a sample of pp interactions at s = 2.76 TeV corresponding to an integrated luminosity of 231 nb - 1 . The individual W + and W - yields in PbPb and pp collisions are found to agree, once the neutron and proton content in Pb nuclei is taken into account. Likewise, the difference observed in the dependence of the positive and negative muon production on pseudorapidity is consistent with next-to-leading-order perturbative QCD calculations.
The I b differential production cross section and the cross section ratio I ( I A= b ) / I ( I b ) are measured as functions of transverse momentum p T I b and rapidity | y I b | in p p collisions at ...s = 7 TeV using data collected by the CMS experiment at the LHC. The measurements are based on I b decays reconstructed in the exclusive final state J / I I , with the subsequent decays J / I a mu + mu a and I a p I , using a data sample corresponding to an integrated luminosity of 1.9 fb a 1 . The product I ( I b ) X B ( I b a J / I I ) versus p T I b falls faster than that of b mesons. The measured value of I ( I b ) X B ( I b a J / I I ) for p T I b > 10 GeV and | y I b | < 2.0 is 1.16 +/- 0.06 +/- 0.12 nb , and the integrated I ( I A= b ) / I ( I b ) ratio is 1.02 +/- 0.07 +/- 0.09 , where the uncertainties are statistical and systematic, respectively.
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