16 research outputs found

    Physics of the HL-LHC, and Perspectives at the HE-LHC

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    Searches for supersymmetry based on events with b jets and four W bosons in pp collisions at 8 TeV

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    Five mutually exclusive searches for supersymmetry are presented based on events in which b jets and four W bosons are produced in proton-proton collisions at root s = 8TeV. The data, corresponding to an integrated luminosity of 19.5 fb(-1), were collected with the CMS experiment at the CERN LHC in 2012. The five studies differ in the leptonic signature from the W boson decays, and correspond to all-hadronic, single-lepton, opposite-sign dilepton, same-sign dilepton, and >= 3 lepton final states. The results of the five studies are combined to yield 95% confidence level limits for the gluino and bottom-squark masses in the context of gluino and bottom-squark pair production, respectively. In the limit when the lightest supersymmetric particle is light, gluino and bottom squark masses are excluded below 1280 and 570 GeV, respectively

    Measurement of the production cross section for a W boson and two b jets in pp collisions at root s=7 TeV

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    The production cross section for a Wboson and two b jets is measured using proton-proton collisions at v root s = 7 TeV in a data sample collected with the CMS experiment at the LHC corresponding to an integrated luminosity of 5.0 fb(-1). The W + bbevents are selected in the W..decay mode by requiring a muon with transverse momentum pT> 25GeVand pseudorapidity |eta| 25GeVand |eta| < 2.4. The measured W + bbproduction cross section in the fiducial region, calculated at the level of final-state particles, is s(pp. W + bb) xB(W..) = 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 usingMadGraphandpythia

    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, Gamma(H), 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 5.1 fb(-1) at a center-of-mass energy root s = 7 TeV and 19.7 fb(-1) at root s = 8 TeV. 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 Gamma(H) < 22 MeV at a 95% confidence level, which is 5.4 times the expected value in the standard model at the measured mass of m(H) = 125.6 GeV

    Search for supersymmetry in pp collisions at in events with a single lepton, large jet multiplicity, and multiple b jets

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    Results are reported from a search for supersymmetry in pp 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(-1) recorded 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 masses

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

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    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 root s = 8 TeVcollected in 2012 with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 19.5 fb(-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 (t) over tilde (2) decaying to a lighter top-squark mass eigenstate (t) over tilde (1) via either (t) over tilde (2) -> H (t) over tilde (1) or (t) over tilde (2) -> Z (t) over tilde (1), followed in both cases by (t) over tilde (1) -> t (chi) over tilde (0)(1), where (chi) over tilde (0)(1) is an undetected, stable, lightest supersymmetric particle. The interpretation is performed in the region where the mass difference between the (t) over tilde (1) and (chi) over tilde (0)(1) states is approximately equal to the top-quark mass (m((t) over tilde )1) - m((chi) over tilde 10) similar or equal to m(t)) which is not probed by searches for direct (t) over tilde (1) squark pair production. The analysis excludes top squarks with masses m((t) over tilde2) 1) < 400 GeVat a 95% confidence level

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

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    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 (t) over bar dilepton final state with proton-proton collision data at root 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 > 0.955 at the 95% confidence level is obtained after requiring R 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, Gamma(t) = 1.36 +/- 0.02 (stat.)(-0.11)(+0.14) (syst.) GeV

    Koulutusluokitus : Koulutuskoodimuutokset vuonna 1989, Liite 3

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    A measurement of inclusive ZZ production cross section and constraints on anomalous triple gauge couplings in proton-proton collisions at s\sqrt{s} = 8 TeV are presented. A data sample, corresponding to an integrated luminosity of 19.6 inverse-femtobarns was collected with the CMS experiment at the LHC. The measurements are performed in the leptonic decay modes ZZllllZZ \to lll'l', where l=e,μl = e, \mu and l=e,μ,τl' = e, \mu, \tau. The measured total cross section, σ(ppZZ)=7.7±0.5(stat.)0.4+0.5(syst.)±0.4(theo.)±0.2(lum.)pb\sigma (pp \to ZZ) = 7.7 \pm 0.5 (stat.)^{+0.5}_{-0.4} (syst.) \pm 0.4 (theo.) \pm 0.2 (lum.) pb for both Z bosons produced in the mass range mZm_Z within 60 and 120 GeV, is consistent with standard model predictions. Differential cross sections are measured and well described by the theoretical predictions. The invariant mass distribution of the four-lepton system is used to set limits on anomalous ZZZ and ZZγ\gamma couplings at the 95% confidence level: f4Zf_4^Z in (-0.004,+0.004), f5Zf_5^Z in (-0.005,+0.005), f4γf_4^\gamma in (-0.004,+0.004), and f5γf_5^\gamma in (-0.005,+0.005)

    Description and performance of track and primary-vertex reconstruction with the CMS tracker

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    A description is provided of the software algorithms developed for the CMS tracker both for reconstructing charged-particle trajectories in proton-proton interactions and for using the resulting tracks to estimate the positions of the LHC luminous region and individual primary-interaction vertices. Despite the very hostile environment at the LHC, the performance obtained with these algorithms is found to be excellent. For t (t) over bar events under typical 2011 pileup conditions, the average track-reconstruction efficiency for promptly-produced charged particles with transverse momenta of p(T) > 0.9GeV is 94% for pseudorapidities of vertical bar eta vertical bar < 0.9 and 85% for 0.9 < vertical bar eta vertical bar < 2.5. The inefficiency is caused mainly by hadrons that undergo nuclear interactions in the tracker material. For isolated muons, the corresponding efficiencies are essentially 100%. For isolated muons of p(T) = 100GeV emitted at vertical bar eta vertical bar < 1.4, the resolutions are approximately 2.8% in p(T), and respectively, 10 m m and 30 mu m in the transverse and longitudinal impact parameters. The position resolution achieved for reconstructed primary vertices that correspond to interesting pp collisions is 10-12 mu m in each of the three spatial dimensions. The tracking and vertexing software is fast and flexible, and easily adaptable to other functions, such as fast tracking for the trigger, or dedicated tracking for electrons that takes into account bremsstrahlung

    Search for pair production of third-generation scalar leptoquarks and top squarks in proton-proton collisions at v root s=8 TeV

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    A search for pair production of third-generation scalar leptoquarks and supersymmetric top quark partners, top squarks, in final states involving tau leptons and bottom quarks is presented. The search uses events from a data sample of proton-proton collisions corresponding to an integrated luminosity of 19.7 fb(-1), collected with the CMS detector at the LHC with root s = 8 TeV. The number of observed events is found to be in agreement with the expected standard model background. Third-generation scalar leptoquarks with masses below 740 GeV are excluded at 95% confidence level, assuming a 100% branching fraction for the leptoquark decay to a tau lepton and a bottom quark. In addition, this mass limit applies directly to top squarks decaying via an R-parity violating coupling. lambda(') (333). The search also considers a similar signature from top squarks undergoing a chargino-mediated decay involving the Rparity violating coupling. lambda(')(3jk). Each top squark decays to a tau lepton, a bottom quark, and two light quarks. Top squarks in this model with masses below 580 GeV are excluded at 95% confidence level. The constraint on the leptoquark mass is the most stringent to date, and this is the first search for top squarks decaying via. lambda(')(3jk)
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