4,539 research outputs found

    Search for B0s → ÎŒ+Ό− and B0 → ÎŒ+Ό− decays with the CMS detector

    Get PDF
    The study of extremely rare or forbidden processes allows the indirect search for new physics through the comparison with the standard model expectations. The leptonic decays of B0s and B0 mesons are flavor changing neutral currents processes highly suppressed in the standard model, with small predicted branching fractions. A search for the rare decays B0s (B0) → ÎŒ+Ό− is performed in pp collisions at √s = 7TeV, with a data sample corresponding to an integrated luminosity of 5 fb−1 collected by the CMS experiment at the LHC. The number of observed events is consistent with the background plus standard model signal expectation. The resulting upper limits on the branching fractions are B(B0s → ÎŒ+Ό−) < 7.7 × 10−9 and B(B0 → ÎŒ+Ό−) < 1.8 × 10−9 at 95% confidence level

    Dark Matter search at LHC

    Get PDF
    The results of recent searches for dark matter performed with the ïŹrst data collected during the CERN LHC Run-2 by the CMS and ATLAS Collaborations, corresponding to 2.1fb−1 and 3.2fb−1 of proton-proton collisions at √s = 13TeV, respectively, are presented and categorized according to the event topology characteristics. No excesses are found above the standard model expectations and the results are interpreted in terms of upper limits in the production of dark matter using simpliïŹed theory models. The results are also translated into limits on the dark matter-nucleon spin-dependent and spin-independent cross section to compare with the results of direct detection experiments

    Combined search for the quarks of a sequential fourth generation

    Get PDF
    Results are presented from a search for a fourth generation of quarks produced singly or in pairs in a data set corresponding to an integrated luminosity of 5 inverse femtobarns recorded by the CMS experiment at the LHC in 2011. A novel strategy has been developed for a combined search for quarks of the up and down type in decay channels with at least one isolated muon or electron. Limits on the mass of the fourth-generation quarks and the relevant Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a simple extension of the standard model with a sequential fourth generation of fermions. The existence of mass-degenerate fourth-generation quarks with masses below 685 GeV is excluded at 95% confidence level for minimal off-diagonal mixing between the third- and the fourth-generation quarks. With a mass difference of 25 GeV between the quark masses, the obtained limit on the masses of the fourth-generation quarks shifts by about +/- 20 GeV. These results significantly reduce the allowed parameter space for a fourth generation of fermions.Comment: Replaced with published version. Added journal reference and DO

    Measurement of the t t-bar production cross section in the dilepton channel in pp collisions at sqrt(s) = 7 TeV