Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(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 sqrt(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 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-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 bbbar-dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final version published in European Physical Journal

Observation of the suppressed ADS modes B →[πKππ]DKand B →[πKππ]Dπ

An analysis of B → DK and B → Dπ decays is presented where the D meson is reconstructed in the four-body nal state Kπππ. Using LHCb data corresponding to an integrated luminosity of 1.0fb1, rst observations are made of the suppressed ADS modes B →[πKππ]D K and B → [πKππ]Dπ with a signicance of 5.1σ and greater than 10σ, respectively. Measurements of CP asymmetries and CP-conserving ratios of partial widths from this family of decays are also performed. The magnitude of the ratio between the suppressed and favoured B → DK amplitudes is determined to be r = 0.097 ±0.011. © 2013 CERN. Published by Elsevier B.V

Search for CP violation in D+ -&gt; phi pi+ and Ds+ -&gt; Ks pi+ decays

A search for CP violation in D+ -&gt; phi pi+ decays is performed using data collected in 2011 by the LHCb experiment corresponding to an integrated luminosity of 1.0 fb^{-1} at a centre of mass energy of 7 TeV. The CP-violating asymmetry is measured to be (-0.04+/-0.14+/-0.14)% for candidates with K-K+ mass within 20 MeV/c^{2} of the phi meson mass. A search for a CP-violating asymmetry that varies across the phi mass region of the D+ -&gt; K-K+pi+ Dalitz plot is also performed, and no evidence for CP violation is found. In addition, the CP asymmetry in the Ds+ -&gt; Ks pi+ decay is measured to be (0.61+/-0.83+/-0.14)%

Observation of the suppressed ADS modes B →[πKππ]DKand B →[πKππ]Dπ

An analysis of B → DK and B → Dπ decays is presented where the D meson is reconstructed in the four-body nal state Kπππ. Using LHCb data corresponding to an integrated luminosity of 1.0fb1, rst observations are made of the suppressed ADS modes B →[πKππ]D K and B → [πKππ]Dπ with a signicance of 5.1σ and greater than 10σ, respectively. Measurements of CP asymmetries and CP-conserving ratios of partial widths from this family of decays are also performed. The magnitude of the ratio between the suppressed and favoured B → DK amplitudes is determined to be r = 0.097 ±0.011. © 2013 CERN. Published by Elsevier B.V

Search for the decay Bs -&gt; D*-+ π+-

A search for the decay Bs -&gt; D*-+ \pi+- is presented using a data sample corresponding to an integrated luminosity of 1.0 fb-1 of pp collisions collected by LHCb. This decay is expected to be mediated by a W-exchange diagram, with little contribution from rescattering processes, and therefore a measurement of the branching fraction will help to understand the mechanism behind related decays such as Bs -&gt; \pi+ \pi- and Bs -&gt; D Dbar. Systematic uncertainties are minimised by using B0 -&gt; D*-+ \pi+- as a normalisation channel. We find no evidence for a signal, and set an upper limit on the branching fraction of BR(Bs -&gt; D*-+ \pi+-) &lt; 6.1 (7.8) x10^(-6) at 90% (95%) confidence level

Performance of the ATLAS Detector using First Collision Data

More than half a million minimum-bias events of LHC collision data were collected by the ATLAS experiment in December 2009 at centre-of-mass energies of 0.9 TeV and 2.36 TeV. This paper reports on studies of the initial performance of the ATLAS detector from these data. Comparisons between data and Monte Carlo predictions are shown for distributions of several track- and calorimeter-based quantities. The good performance of the ATLAS detector in these first data gives confidence for successful running at higher energies

Measurement of the inclusive isolated prompt photon cross section in pp collisions at √s=7 TeV with the ATLAS detector

A measurement of the cross section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy [sqrt]s=7  TeV is presented. The measurement covers the pseudorapidity ranges |etaγ|<1.37 and 1.52≤|etaγ|<1.81 in the transverse energy range 15≤ETγ<100  GeV. The results are based on an integrated luminosity of 880  nb-1, collected with the ATLAS detector at the Large Hadron Collider. Photon candidates are identified by combining information from the calorimeters and from the inner tracker. Residual background in the selected sample is estimated from data based on the observed distribution of the transverse isolation energy in a narrow cone around the photon candidate. The results are compared to predictions from next-to-leading-order perturbative QCD calculations.United States. Dept. of EnergyNational Science Foundation (U.S.