TY - JOUR T1 - Search for light scalar top-quark pair production in final states with two leptons with the ATLAS detector in √s=7 TeV proton–proton collisions JF - The European Physical Journal C N2 - A search is presented for the pair production of light scalar top quarks in √s=7 TeV proton–proton collisions recorded with the ATLAS detector at the Large Hadron Collider. This analysis uses the full data sample collected during 2011 running that corresponds to a total integrated luminosity of 4.7 fb\(^{−1}\). Light scalar top quarks are searched for in events with two opposite-sign leptons (e, μ), large missing transverse momentum and at least one jet in the final state. No excess over Standard Model expectations is found, and the results are interpreted under the assumption that the light scalar top decays to a b-quark in addition to an on-shell chargino whose decay occurs through a virtual W boson. If the chargino mass is 106 GeV, light scalar top-quark masses up to 130 GeV are excluded for neutralino masses below 70 GeV. KW - signal cross section KW - jet energy scale KW - jet energy scale uncertainty KW - dead region KW - jet energy resolution KW - top quark pair KW - charingo mass KW - top quark decay KW - SM background KW - simulaed event sample KW - MC simulation KW - visible cross section KW - anti-k jet KW - top event dilepton invariant mass Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-129561 VL - 72 IS - 2237 ER - TY - JOUR T1 - Search for supersymmetry in events with large missing transverse momentum, jets, and at least one tau lepton in 7 TeV proton-proton collision data with the JF - The European Physical Journal C N2 - A search for supersymmetry (SUSY) in events with large missing transverse momentum, jets, and at least one hadronically decaying τ lepton, with zero or one additional light lepton (e/μ), has been performed using 4.7 fb\(^{−1}\) of proton-proton collision data at \(\sqrt s\)=7TeV recorded with the ATLAS detector at the Large Hadron Collider. No excess above the Standard Model background expectation is observed and a 95 % confidence level visible cross-section upper limit for new phenomena is set. In the framework of gauge-mediated SUSY-breaking models, lower limits on the mass scale Λ are set at 54 TeV in the regions where the \(\tilde τ_1\) is the next-to-lightest SUSY particle (tanβ>20). These limits provide the most stringent tests to date of GMSB models in a large part of the parameter space considered. KW - multi-jet background KW - jet energy scale KW - systematic uncertainty KW - jet background KW - anti-k jet KW - jet energy resolution KW - MC expectation KW - GMSB model KW - Cl Lowe limit KW - transverse momentum KW - single top event KW - SM background KW - MC simulation KW - transverse momentum vector KW - SUSY breaking scale Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-128891 VL - 72 IS - 2215 ER - TY - JOUR T1 - Measurement of the charge asymmetry in top quark pair production in pp collisions at √s=7 TeV using the ATLAS detector JF - The European Physical Journal C N2 - A measurement of the top-antitop production charge asymmetry A C is presented using data corresponding to an integrated luminosity of 1.04 fb\(^{−1}\) of pp collisions at √s=7 TeV collected by the ATLAS detector at the LHC. Events are selected with a single lepton (electron or muon), missing transverse momentum and at least four jets of which at least one jet is identified as coming from a b-quark. A kinematic fit is used to reconstruct the t\(\overline t\) event topology. After background subtraction, a Bayesian unfolding procedure is performed to correct for acceptance and detector effects. The measured value of A\(_C\) is AC=−0.019±0.028 (stat.)±0.024 (syst.), consistent with the prediction from the MC@NLO Monte Carlo generator of A\(_C\) =0.006±0.002. Measurements of A\(_C\) in two ranges of invariant mass of the top-antitop pair are also shown. KW - jet multiplicity KW - B-tagged jet KW - systematic uncertainty KW - jet energy resolution KW - top quark masse KW - muon channel KW - jet scale energy KW - light quark jet KW - heavy flavour KW - single top production KW - single top event KW - fake lepton KW - top quark pair KW - multijet background KW - JES Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-128904 VL - 72 IS - 2039 ER - TY - JOUR T1 - Measurement of \(t\overline t\) production with a veto on additional central jet activity in pp collisions at √s=7 TeV using the ATLAS detector JF - European Physical Journal C N2 - A measurement of the jet activity in \(t\overline t\) events produced in proton–proton collisions at a centre-of-mass energy of 7 TeV is presented, using 2.05 fb\(^{−1}\) of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. The \(t\overline t\) events are selected in the dilepton decay channel with two identified b-jets from the top quark decays. Events are vetoed if they contain an additional jet with transverse momentum above a threshold in a central rapidity interval. The fraction of events surviving the jet veto is presented as a function of this threshold for four different central rapidity interval definitions. An alternate measurement is also performed, in which events are vetoed if the scalar transverse momentum sum of the additional jets in each rapidity interval is above a threshold. In both measurements, the data are corrected for detector effects and compared to the theoretical models implemented in MC@NLO, Powheg, Alpgen and Sherpa. The experimental uncertainties are often smaller than the spread of theoretical predictions, allowing deviations between data and theory to be observed in some regions of phase space. KW - jet reconstruction efficiency KW - jet energy scale KW - jet energy scale uncertainty KW - fiducial cross section KW - individual systematic uncertainty KW - jet energy resolution KW - systematic uncertainty KW - muon reconstruction efficiency KW - rapidity interval KW - pythia parton shower KW - jet transverse momentum KW - underlying event tune KW - particle level jet KW - additional jet KW - MC event generator Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-128931 VL - 72 IS - 2043 ER -