Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at root s=7 TeV with the ATLAS detector

"The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass energy of root s = 7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb(-1). The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the range 20 -dijet cross-section is measured as a function of the dijet invariant mass in the range 110 < m(jj) < 760 GeV, the azimuthal angle difference between the two jets and the angular variable chi in two dijet mass regions. The results are compared with next-to-leading-order QCD predictions. Good agreement is observed between the measured cross-sections and the predictions obtained using POWHEG + Pythia. MC@NLO + Herwig shows good agreement with the measured b (b) over bar -dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta. RI Gutierrez, Phillip\/C-1161-2011; Ferrando, James\/A-9192-2012; collins-tooth, christopher\/A-9201-2012; Perrino, Roberto\/B-4633-2010; Laurelli, Paolo\/B-1432-2012; De Cecco, Sandro\/B-1016-2012; Stoicea, Gabriel\/B-6717-2011; branchini, paolo\/A-4857-2011; Wolter, Marcin\/A-7412-2012; Rotaru, Marina\/A-3097-2011; O'Shea, Val\/G-1279-2010; Doyle, Anthony\/C-5889-2009; Buttar, Craig\/D-3706-2011; Pina, Joao \/C-4391-2012; Takai, Helio\/C-3301-2012; St.Denis, Richard\/C-8997-2012; Jones, Roger\/H-5578-2011; Britton, David\/F-2602-2010; Li, Xuefei\/C-3861-2012; Fazio, Salvatore \/G-5156-2010; Smirnova, Lidia\/D-8089-2012; Smirnov, Sergei\/F-1014-2011; Gladilin, Leonid\/B-5226-2011; Barreiro, Fernando\/D-9808-2012; Kramarenko, Victor\/E-1781-2012; Prokoshin, Fedor\/E-2795-2012; Alexa, Calin\/F-6345-2010; Pacheco Pages, Andres\/C-5353-2011; Moorhead, Gareth\/B-6634-2009; Livan, Michele\/D-7531-2012; Petrucci, Fabrizio\/G-8348-2012; Wemans, Andre\/A-6738-2012; Fabbri, Laura\/H-3442-2012; Kurashige, Hisaya\/H-4916-2012; Villa, Mauro\/C-9883-2009; Kuzhir, Polina\/H-8653-2012; Delmastro, Marco\/I-5599-2012

Search for supersymmetry in final states with jets, missing transverse momentum and one isolated lepton in root s=7 TeV pp collisions using 1 fb(-1) of ATLAS data

We present an update of a search for supersymmetry in final states containing jets, missing transverse momentum, and one isolated electron or muon, using 1.04 fb(-1) of proton-proton collision data at root s =7 TeV recorded by the ATLAS experiment at the LHC in the first half of 2011. The analysis is carried out in four distinct signal regions with either three or four jets and variations on the (missing) transverse momentum cuts, resulting in optimized limits for various supersymmetry models. No excess above the standard model background expectation is observed. Limits are set on the visible cross section of new physics within the kinematic requirements of the search. The results are interpreted as limits on the parameters of the minimal supergravity framework, limits on cross sections of simplified models with specific squark and gluino decay modes, and limits on parameters of a model with bilinear R-parity violation

Search for anomaly-mediated supersymmetry breaking with the ATLAS detector based on a disappearing-track signature in pppp collisions at s\sqrt{s} = 7 TeV

In models of anomaly-mediated supersymmetry breaking (AMSB), the lightest chargino is predicted to have a lifetime long enough to be detected in collider experiments. This letter explores AMSB scenarios in pp collisions at sqrt(s) = 7 TeV by attempting to identify decaying charginos which result in tracks that appear to have few associated hits in the outer region of the tracking system. The search was based on data corresponding to an integrated luminosity of 1.02 fb^-1 collected with the ATLAS detector in 2011. The pT spectrum of candidate tracks is found to be consistent with the expectation from Standard Model background processes and constraints on the lifetime and the production cross section were obtained. In the minimal AMSB framework with m_3/2 < 32 TeV, m_0 < 1.5 TeV, tan(beta) = 5 and mu > 0, a chargino having mass below 92 GeV and a lifetime between 0.5 ns and 2 ns is excluded at 95% confidence level.Comment: 7 pages plus author list (20 pages total), 8 figures, 2 tables, revised author list, matches Eur. Phys. J. C versio

Properties of jets measured from tracks in proton-proton collisions at center-of-mass energy root s=7 TeV with the ATLAS detector

"Jets are identified and their properties studied in center-of-mass energy root s = 7 TeV proton-proton collisions at the Large Hadron Collider using charged particles measured by the ATLAS inner detector. Events are selected using a minimum bias trigger, allowing jets at very low transverse momentum to be observed and their characteristics in the transition to high-momentum fully perturbative jets to be studied. Jets are reconstructed using the anti-k(t) algorithm applied to charged particles with two radius parameter choices, 0.4 and 0.6. An inclusive charged jet transverse momentum cross section measurement from 4 GeV to 100 GeV is shown for four ranges in rapidity extending to 1.9 and corrected to charged particle-level truth jets. The transverse momenta and longitudinal momentum fractions of charged particles within jets are measured, along with the charged particle multiplicity and the particle density as a function of radial distance from the jet axis. Comparison of the data with the theoretical models implemented in existing tunings of Monte Carlo event generators indicates reasonable overall agreement between data and Monte Carlo. These comparisons are sensitive to Monte Carlo parton showering, hadronization, and soft physics models.