Search for supersymmetry in pp collisions at View the MathML sources=8 TeV in events with a single lepton, large jet multiplicity, and multiple b jets

Results are reported from a search for supersymmetry in pppp collisions at a center-of-mass energy of 8 TeV, based on events with a single isolated lepton (electron or muon) and multiple jets, at least two of which are identified as b jets. The data sample corresponds to an integrated luminosity of 19.3 fb−1recorded by the CMS experiment at the LHC in 2012. The search is motivated by supersymmetric models that involve strong-production processes and cascade decays of new particles. The resulting final states contain multiple jets as well as missing transverse momentum from weakly interacting particles. The event yields, observed across several kinematic regions, are consistent with the expectations from standard model processes. The results are interpreted in the context of simplified supersymmetric scenarios with pair production of gluinos, where each gluino decays to a top quark–antiquark pair and the lightest neutralino. For the case of decays via virtual top squarks, gluinos with a mass smaller than 1.26 TeV are excluded for low neutralino masse

Modification of jet shapes in PbPb collisions at √ sNN = 2.76 TeV

The first measurement of jet shapes, defined as the fractional transverse momentum radial distribution, for inclusive jets produced in heavy-ion collisions is presented. Data samples of PbPb and pp collisions, corresponding to integrated luminosities of 150 μb−1 and 5.3 pb−1 respectively, were collected at a nucleon–nucleon centre-of-mass energy of √ sNN = 2.76 TeV with the CMS detector at the LHC. The jets are reconstructed with the anti-kT algorithm with a distance parameter R = 0.3, and the jet shapes are measured for charged particles with transverse momentum pT \u3e 1 GeV/c. The jet shapes measured in PbPb collisions in different collision centralities are compared to reference distributions based on the pp data. A centrality-dependent modification of the jet shapes is observed in the more central PbPb collisions, indicating a redistribution of the energy inside the jet cone. This measurement provides information about the parton shower mechanism in the hot and dense medium produced in heavy-ion collisions

Search for baryon number violation in top-quark decays

A search for baryon number violation (BNV) in top-quark decays is performed using pp collisions produced by the LHC at √ s = 8 TeV. The top-quark decay considered in this search results in one light lepton (muon or electron), two jets, but no neutrino in the final state. Data used for the analysis were collected by the CMS detector and correspond to an integrated luminosity of 19.5 fb−1. The event selection is optimized for top quarks produced in pairs, with one undergoing the BNV decay and the other the standard model hadronic decay to three jets. No significant excess of events over the expected yield from standard model processes is observed. The upper limits at 95% confidence level on the branching fraction of the BNV top-quark decay are calculated to be 0.0016 and 0.0017 for the muon and the electron channels, respectively. Assuming lepton universality, an upper limit of 0.0015 results from the combination of the two channels. These limits are the first that have been obtained on a BNV process involving the top quark

Differential cross section measurements for the production of aWboson in association with jets in proton–proton collisions at √s=7TeV

Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0fb−1. The measured cross sections are compared to predictions from Monte Carlo generators,MadGraph+pythiaandsherpa, and to next-to-leading-order calculations fromBlackHat+sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pTdistributions of the leading jets at high pTvalues, the distributions of the HTat high-HTand low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values

Searches for light- and heavy-flavour three-jet resonances in pp collisions at √ s = 8 TeV

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 19.4 fb−1. 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

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

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 t¯tdilepton final state with proton–proton collision data at √s=8TeVfrom an integrated luminosity of 19.7fb−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 \u3e0.955at the 95% confidence level is obtained after requiring R ≤1, and a lower limit on the Cabibbo–Kobayashi–Maskawa matrix element |Vtb| \u3e0.975is 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, Γt=1.36 ±0.02 (stat.)+0.14−0.11(syst.)GeV

Measurement of the pp→ZZproduction cross section and constraints on anomalous triple gauge couplings in four-lepton final states at √s=8TeV

A measurement of the inclusive ZZproduction cross section and constraints on anomalous triple gauge couplings in proton–proton collisions at √s=8TeVare presented. The analysis is based on a data sample, corresponding to an integrated luminosity of 19.6fb−1, collected with the CMS experiment at the LHC. The measurements are performed in the leptonic decay modes ZZ →, where=e, μand =e, μ, τ. The measured total cross section σ(pp →ZZ) =7.7 ±0.5(stat)+0.5−0.4(syst)±0.4 (theo) ±0.2(lumi)pb, for both Zbosons produced in the mass range 6

Measurement of the production cross section for a Wboson and two bjets in ppcollisions at √s=7TeV

The production cross section for a Wboson and two b jets is measured using proton–proton collisions at √s=7TeVin a data sample collected with the CMS experiment at the LHC corresponding to an integrated luminosity of 5.0fb−1. The W +bbevents are selected in the W →μνdecay mode by requiring a muon with transverse momentum pT\u3e25GeVand pseudorapidity |η| \u3c2.1, and exactly two b-tagged jets with pT\u3e25GeVand |η| \u3c2.4. The measured W +bbproduction cross section in the fiducial region, calculated at the level of final-state particles, is σ(pp →W +bb) ×B(W →μν) =0.53 ±0.05 (stat.)±0.09 (syst.)±0.06 (theo.)±0.01 (lum.)pb, in agreement with the standard model prediction. In addition, kinematic distributions of the W +bbsystem are in agreement with the predictions of a simulation using MadGraph and pythia

Search for top-squark pairs decaying into Higgs or Z bosons in pp collisions at √s=8TeV

A search for supersymmetry through the direct pair production of top squarks, with Higgs (H) or Z bosons in the decay chain, is performed using a data sample of proton–proton collisions at √s=8TeVcollected in 2012 with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 19.5fb−1. The search is performed using a selection of events containing leptons and bottom-quark jets. No evidence for a significant excess of events over the standard model background prediction is observed. The results are interpreted in the context of simplified supersymmetric models with pair production of a heavier top-squark mass eigenstate ˜ t2decaying to a lighter top-squark mass eigenstate ˜t1via either ˜t2→H˜ t1or ˜t2→Z˜ t1, followed in both cases by ˜t1→t˜ χ01, where ˜ χ01is an undetected, stable, lightest supersymmetric particle. The interpretation is performed in the region where the mass difference between the ˜ t1and ˜ χ01states is approximately equal to the top-quark mass (m˜ t1−m˜ χ01mt), which is not probed by searches for direct ˜ t1squark pair production. The analysis excludes top squarks with masses m˜ t2\u3c575GeVand m˜ t1\u3c400GeVat a 95% confidence level

Observation of a peaking structure in the J/ψφmass spectrum from B±→J/ψφK±decays

A peaking structure in the J/ψφmass spectrum near threshold is observed in B±→J/ψφK±decays, produced in pp collisions at √s=7TeVcollected with the CMS detector at the LHC. The data sample, selected on the basis of the dimuon decay mode of the J/ψ, corresponds to an integrated luminosity of 5.2fb−1. Fitting the structure to an S-wave relativistic Breit–Wigner lineshape above a three-body phase-space nonresonant component gives a signal statistical significance exceeding five standard deviations. The fitted mass and width values are m =4148.0 ±2.4 (stat.) ±6.3 (syst.) MeVand Γ=28+15−11(stat.) ±19 (syst.) MeV, respectively. Evidence for an additional peaking structure at higher J/ψφmass is also reported