Electron reconstruction and identification efficiency measurements with the ATLAS detector using the 2011 LHC proton–proton collision data

Many of the interesting physics processes to be measured at the LHC have a signature involving one or more isolated electrons. The electron reconstruction and identification efficiencies of the ATLAS detector at the LHC have been evaluated using proton–proton collision data collected in 2011 at s√=7 TeV and corresponding to an integrated luminosity of 4.7 fb −1. Tag-and-probe methods using events with leptonic decays of W and Z bosons and J/ψ mesons are employed to benchmark these performance parameters. The combination of all measurements results in identification efficiencies determined with an accuracy at the few per mil level for electron transverse energy greater than 30 GeV

Monitoring and data quality assessment of the ATLAS liquid argon calorimeter

The liquid argon calorimeter is a key component of the ATLAS detector installed at the CERN Large Hadron Collider. The primary purpose of this calorimeter is the measurement of electron and photon kinematic properties. It also provides a crucial input for measuring jets and missing transverse momentum. An advanced data monitoring procedure was designed to quickly identify issues that would affect detector performance and ensure that only the best quality data are used for physics analysis. This article presents the validation procedure developed during the 2011 and 2012 LHC data-taking periods, in which more than 98% of the proton-proton luminosity recorded by ATLAS at a centre-of-mass energy of 7-8 TeV had calorimeter data quality suitable for physics analysis

Flavor tagged time-dependent angular analysis of the B-s(0) -> J/psi phi decay and extraction of Delta Gamma(s) and the weak phase phi(s) in ATLAS

A measurement of the B-s(0) -> J/psi phi decay parameters, updated to include flavor tagging is reported using 4.9 fb(-1) of integrated luminosity collected by the ATLAS detector from root s = 7 TeV pp collisions recorded in 2011 at the LHC. The values measured for the physical parameters are phi(s) = 0.12 +/- 0.25(stat) +/- 0.05(syst) rad Delta Gamma(s) = 0.053 +/- 0.021(stat) +/- 0.010(syst) ps(-1) Gamma(s) = 0.677 +/- 0.007(stat) +/- 0.004(syst) ps(-1) vertical bar A(parallel to)(0)vertical bar(2) = 0.220 +/- 0.008(stat) +/- 0.009(syst) vertical bar A(0)(0)vertical bar(2) = 0.529 +/- 0.006(stat) +/- 0.012(syst) delta(perpendicular to) = 3.89 +/- 0.47(stat) +/- 0.11(syst) rad where the parameter Delta Gamma(s) is constrained to be positive. The S-wave contribution was measured and found to be compatible with zero. Results for phi(s) and Delta Gamma(s) are also presented as 68% and 95% likelihood contours, which show agreement with the Standard Model expectations

Search for top quark decays t -> q H with H -> gamma gamma using the ATLAS detector

A search is performed for flavour-changing neutral currents in the decay of a top quark to an up-type (c, u) quark and a Higgs boson, where the Higgs boson decays to two photons. The proton-proton collision data set used corresponds to 4.7 fb(-1) at root s = 7TeV and 20.3 fb(-1) at root s = 8TeV collected by the ATLAS experiment at the LHC. Top quark pair events are searched for in which one top quark decays to qH and the other decays to bW. Both the hadronic and the leptonic decay modes of the W boson are used. No significant signal is observed and an upper limit is set on the t -> qH branching ratio of 0.79% at the 95% confidence level. The corresponding limit on the tqH coupling combination root lambda(2)(tcH) + root lambda(2)(tuH) is 0.17

Study of heavy-flavor quarks produced in association with top-quark pairs at root s=7 TeV using the ATLAS detector

Contains fulltext : 127840.pdf (preprint version ) (Open Access

Measurements of W gamma and Z gamma production in pp collisions at root s=7 TeV with the ATLAS detector at the LHC

"The integrated and differential fiducial cross sections for the production of a W or Z boson in association with a high-energy photon are measured using pp collisions at root s = 7 TeV. The analyses use a data sample with an integrated luminosity of 4.6 fb(-1) collected by the ATLAS detector during the 2011 LHC data-taking period. Events are selected using leptonic decays of the W and Z bosons [W(e nu, mu nu) and Z(e(+)e(-), mu(+)mu(-), nu(nu) over bar)] with the requirement of an associated isolated photon. The data are used to test the electroweak sector of the Standard Model and search for evidence for new phenomena. The measurements are used to probe the anomalous WW gamma, ZZ gamma, and Z gamma gamma triple-gauge-boson couplings and to search for the production of vector resonances decaying to Z gamma and W gamma. No deviations from Standard Model predictions are observed and limits are placed on anomalous triple-gauge-boson couplings and on the production of new vector meson resonances.

Muon reconstruction efficiency and momentum resolution of the ATLAS experiment in proton-proton collisions at root s = 7 TeV in 2010

This paper presents a study of the performance of the muon reconstruction in the analysis of proton–proton collisions at √s = 7 TeV at the LHC, recorded by the ATLAS detector in 2010. This performance is described in terms of reconstruction and isolation efficiencies and momentum resolutions for different classes of reconstructed muons. The results are obtained from an analysis of J/ψ meson and Z boson decays to dimuons, reconstructed from a data sample corresponding to an integrated luminosity of 40 pb⁻¹. The measured performance is compared to Monte Carlo predictions and deviations from the predicted performance are discussed.G. Aad … P. Jackson … L. Lee … a. Petridis … N. Soni … M. White .. The ATLAS Collaboratio