ATLAS

Abstract:

The results of a search for pair production of the lighter scalar partners of top quarks (t~1) in 2.05 fb-1 of pp collisions at s=7 TeV using the ATLAS experiment at the LHC are reported. Scalar top quarks are searched for in events with two same flavour opposite-sign leptons (e, μ) with invariant mass consistent with the Z boson mass, large missing transverse momentum and jets in the final state. At least one of the jets is identified as originating from a b-quark. No excess over Standard Model expectations is found. The results are interpreted in the framework of R-parity conserving, gauge mediated Supersymmetry breaking 'natural' scenarios, where the neutralino (χ~10) is the next-to-lightest supersymmetric particle. Scalar top quark masses up to 310 GeV are excluded for 115GeVmZ. © 2012 CERN.

Abstract:

The results of a search for pair production of the lighter scalar partners of top quarks (t~1) in 2.05 fb -1 of pp collisions at s=7 TeV using the ATLAS experiment at the LHC are reported. Scalar top quarks are searched for in events with two same flavour opposite-sign leptons (e, μ) with invariant mass consistent with the Z boson mass, large missing transverse momentum and jets in the final state. At least one of the jets is identified as originating from a b-quark. No excess over Standard Model expectations is found. The results are interpreted in the framework of R-parity conserving, gauge mediated Supersymmetry breaking 'natural' scenarios, where the neutralino (χ~10) is the next-to-lightest supersymmetric particle. Scalar top quark masses up to 310 GeV are excluded for 115GeVmZ. © 2012 CERN.

Abstract:

We present a search for the standard model Higgs boson produced in association with a Z boson, using up to 7.9 fb -1 of integrated luminosity from pp- collisions collected with the CDF II detector. We utilize several novel techniques, including multivariate lepton selection, multivariate trigger parametrization, and a multi-stage signal discriminant consisting of specialized functions trained to distinguish individual backgrounds. By increasing acceptance and enhancing signal discrimination, these techniques have significantly improved the sensitivity of the analysis above what was expected from a larger dataset alone. We observe no significant evidence for a signal, and we set limits on the ZH production cross section. For a Higgs boson with mass 115 GeV/c 2, we expect (observe) a limit of 3.9 (4.8) times the standard model predicted value, at the 95% credibility level. © 2012 Elsevier B.V.

Abstract:

A measurement is presented of W-boson production in PbPb collisions carried out at a nucleon-nucleon (NN) centre-of-mass energy sNN of 2.76 TeV at the LHC using the CMS detector. In data corresponding to an integrated luminosity of 7.3 μb-1, the number of W→μνμ decays is extracted in the region of muon pseudorapidity |ημ|<2.1 and transverse momentum pTμ>25 GeV/c. Yields of muons found per unit of pseudorapidity correspond to (159±10(stat.)±12(syst.))×10-8 W+ and (154±10(stat.)±12(syst.))×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. © 2012 CERN.