Search for physics beyond the standard model in events with two leptons, jets, and missing transverse momentum in pp collisions at √s = 8 TeV

A search is presented for physics beyond the standard model in final states with two opposite-sign same-flavor leptons, jets, and missing transverse momentum. The data sample corresponds to an integrated luminosity of 19.4 fb[superscript −1] of proton-proton collisions at √s = 8 TeV collected with the CMS detector at the CERN LHC in 2012. The analysis focuses on searches for a kinematic edge in the invariant mass distribution of the oppositesign same-flavor lepton pair and for final states with an on-shell Z boson. The observations are consistent with expectations from standard model processes and are interpreted in terms of upper limits on the production of supersymmetric particles.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio

Measurement of the W boson helicity in events with a single reconstructed top quark in pp collisions at √s = 8 TeV

A measurement of the W boson helicity is presented, where the W boson originates from the decay of a top quark produced in pp collisions. The event selection, optimized for reconstructing a single top quark in the final state, requires exactly one isolated lepton (muon or electron) and exactly two jets, one of which is likely to originate from the hadronization of a bottom quark. The analysis is performed using data recorded at a center-of-mass energy of 8 TeV with the CMS detector at the CERN LHC in 2012. The data sample corresponds to an integrated luminosity of 19.7 fb[superscript −1]. The measured helicity fractions are F [subscript L] = 0.298 ± 0.028 (stat) ± 0.032(syst), F [subscript 0] = 0.720 ± 0.039 (stat) ± 0.037(syst), and F [subscript R] = −0.018 ± 0.019 (stat) ± 0.011(syst). These results are used to set limits on the real part of the tWb anomalous couplings, g [subscript L] and g [subscript R]

Search for a standard model Higgs boson produced in association with a top-quark pair and decaying to bottom quarks using a matrix element method

A search for a standard model Higgs boson produced in association with a top-quark pair and decaying to bottom quarks is presented. Events with hadronic jets and one or two oppositely charged leptons are selected from a data sample corresponding to an integrated luminosity of 19.5 fb[superscript -1] collected by the CMS experiment at the LHC in pp collisions at a centre-of-mass energy of 8 TeV. In order to separate the signal from the larger t[bar over t] + jets background, this analysis uses a matrix element method that assigns a probability density value to each reconstructed event under signal or background hypotheses. The ratio between the two values is used in a maximum likelihood fit to extract the signal yield. The results are presented in terms of the measured signal strength modifier, μ, relative to the standard model prediction for a Higgs boson mass of 125 GeV. The observed (expected) exclusion limit at a 95 % confidence level is μ < 4.2 (3.3), corresponding to a best fit value [^ over μ] = 1.2[+1.6 over −1.5].United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio

Search for the production of dark matter in association with top-quark pairs in the single-lepton final state in proton-proton collisions at √s = 8 TeV

A search is presented for particle dark matter produced in association with a pair of top quarks in pp collisions at a centre-of-mass energy of √s = 8 TeV. The data were collected with the CMS detector at the LHC and correspond to an integrated luminosity of 19.7 fb[superscript −1]. This search requires the presence of one lepton, multiple jets, and large missing transverse energy. No excess of events is found above the SM expectation, and upper limits are derived on the production cross section. Interpreting the findings in the context of a scalar contact interaction between fermionic dark matter particles and top quarks, lower limits on the interaction scale are set. These limits are also interpreted in terms of the dark matter-nucleon scattering cross sections for the spin-independent scalar operator and they complement direct searches for dark matter particles in the low mass region.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio

Search for new physics in events with same-sign dileptons and jets in pp collisions at √s = 8 TeV

A search for new physics is performed based on events with jets and a pair of isolated, same-sign leptons. The results are obtained using a sample of proton-proton collision data collected by the CMS experiment at a centre-of-mass energy of 8 TeV at the LHC, corresponding to an integrated luminosity of 19.5 fb[superscript −1]. In order to be sensitive to a wide variety of possible signals beyond the standard model, multiple search regions defined by the missing transverse energy, the hadronic energy, the number of jets and b-quark jets, and the transverse momenta of the leptons in the events are considered. No excess above the standard model background expectation is observed and constraints are set on a number of models for new physics, as well as on the same-sign top-quark pair and quadruple-top-quark production cross sections. Information on event selection efficiencies is also provided, so that the results can be used to confront an even broader class of new physics models.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio

Search for the associated production of the Higgs boson with a top-quark pair

A search for the standard model Higgs boson produced in association with a top-quark pair (tt¯H) is presented, using data samples corresponding to integrated luminosities of up to 5.1 fb−1 and 19.7 fb−1 collected in pp collisions at center-of-mass energies of 7 TeV and 8 TeV respectively. The search is based on the following signatures of the Higgs boson decay: H → hadrons, H → photons, and H → leptons. The results are characterized by an observed tt¯H signal strength relative to the standard model cross section, μ=σ/σ SM,under the assumption that the Higgs boson decays as expected in the standard model. The best fit value is μ = 2.8 ± 1.0 for a Higgs boson mass of 125.6 GeV.National Science Foundation (U.S.

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

A search is performed in proton–proton collisions at √s = 8 TeV for exotic particles decaying via WZ to fully leptonic final states with electrons, muons, and neutrinos. The data set corresponds to an integrated luminosity of 19.5 fb[superscript −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 W′ boson as predicted by an extended gauge model, and on the W′WZ coupling. The expected and observed mass limits for a W′ boson, as predicted by this model, are 1.55 and 1.47 TeV, respectively. Stringent limits are also set in the context of low-scale technicolor models under a range of assumptions for the model parameters.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio

THE ALICE SILICON PIXEL DETECTOR (SPD)

G. ANELLI, F. ANTINORI, A. BOCCARDI, M. BURNS, I. A. CALI, M. CAMPBELL, P. CHOCHULA, R. DINAPOLI, D. ELIA, F. FORMENTI, A. O. GINER, M. KRIVDA, V. LENTI, V. MANZARI, M. MOREL, P. NILSSON, A. PEPATO, P. RIEDLER, R. SANTORO, G. STEFANINI CERN European Organization for Nuclear Research, CH-1211 Geneva 23, Switzerland Universita degli Studi di Padova, I-35131, Padova, Italy Dipartimento IA di Fisica e Sez. INFN di Bari, I-70126, Bari ,Italy Slovak Academy of Sciences, SK-04353, Kosice, Slovakia ASP-Associazione per lo Sviluppo Scientifico e Technologico del Piemonte, I-10133 Torino, Ital

Search for standard model production of four top quarks in the lepton + jets channel in pp collisions at √s = 8 TeV

A search is presented for standard model (SM) production of four top quarks (tt¯tt¯) in pp collisions in the lepton + jets channel. The data correspond to an integrated luminosity of 19.6 fb[superscript −1] recorded at a centre-of-mass energy of 8 TeV with the CMS detector at the CERN LHC. The expected cross section for SM tt¯tt¯ production is σSMtt¯tt¯≈1fb . A combination of kinematic reconstruction and multivariate techniques is used to distinguish between the small signal and large background. The data are consistent with expectations of the SM, and an upper limit of 32 fb is set at a 95% confidence level on the cross section for producing four top quarks in the SM, where a limit of 32 ± 17 fb is expected.National Science Foundation (U.S.)United States. Dept. of Energ

Measurement of the charge ratio of atmospheric muons with the CMS detector

We present a measurement of the ratio of positive to negative muon fluxes from cosmic ray interactions in the atmosphere, using data collected by the CMS detector both at ground level and in the underground experimental cavern at the CERN LHC. Muons were detected in the momentum range from 5 GeV/c to 1 TeV/c . The surface flux ratio is measured to be 1.2766±0.0032(stat.)±0.0032(syst.), independent of the muon momentum, below 100 GeV/c. This is the most precise measurement to date. At higher momenta the data are consistent with an increase of the charge ratio, in agreement with cosmic ray shower models and compatible with previous measurements by deep-underground experiments.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio