Abstract: 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 TeV and corresponding to an integrated luminosity of 4.7 fb. Tag-and-probe methods using events with leptonic decays of and bosons and 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.

Abstract: The integrated elliptic flow of charged particles produced in Pb+Pb collisions at root S-NN = 2.76 TeV has been measured with the ATLAS detector using data collected at the Large Hadron Collider. The anisotropy parameter, upsilon(2), was measured in the pseudorapidity range |eta| <= 2.5 with the event-plane method. In order to include tracks with very low transverse momentum p(T), thus reducing the uncertainty in upsilon(2) integrated over p(T), a 1 μb(-1) data sample recorded without a magnetic field in the tracking detectors is used. The centrality dependence of the integrated upsilon(2) is compared to other measurements obtained with higher PT thresholds. The integrated elliptic flow is weakly decreasing with |eta|. The integrated upsilon 2 transformed to the rest frame of one of the colliding nuclei is compared to the lower-energy RHIC data.

Abstract: The jet energy scale (JES) and its systematic uncertainty are determined for jetsmeasured with the ATLAS detector using proton-proton collision data with a centre-of-mass energy of root s = 7 TeV corresponding to an integrated luminosity of 4.7 fb(-1). Jets are reconstructed from energy deposits forming topological clusters of calorimeter cells using the anti-kt algorithmwith distance parameters R = 0.4 or R = 0.6, and are calibrated using MC simulations. A residual JES correction is applied to account for differences between data and MC simulations. This correction and its systematic uncertainty are estimated using a combination of in situ techniques exploiting the transverse momentum balance between a jet and a reference object such as a photon or a Z boson, for 20 <= p(T)(jet) < 1000 GeV and pseudorapidities vertical bar eta vertical bar < 4.5. The effect of multiple proton-proton interactions is corrected for, and an uncertainty is evaluated using in situ techniques. The smallest JES uncertainty of less than 1% is found in the central calorimeter region (vertical bar eta vertical bar| < 1.2) for jets with 55 = p(T)(jet) < 500 GeV. For central jets at lower p(T), the uncertainty is about 3%. A consistent JES estimate is found using measurements of the calorimeter response of single hadrons in proton-proton collisions and test-beam data, which also provide the estimate for p(T)(jet) > 1 TeV. The calibration of forward jets is derived from dijet p(T) balance measurements. The resulting uncertainty reaches its largest value of 6% for low-p(T) jets at vertical bar eta vertical bar| = 4.5. Additional JES uncertainties due to specific event topologies, such as close-by jets or selections of event samples with an enhanced content of jets originating from light quarks or gluons, are also discussed. The magnitude of these uncertainties depends on the event sample used in a given physics analysis, but typically amounts to 0.5-3%.

Abstract: This paper presents a search for a new heavy particle produced in association with a top or antitop quark. Two models in which the new heavy particle is a color singlet or a color triplet are considered, decaying, respectively, to (t)over-barq or tq, leading to a resonance within the t(t)over-bar + jets signature. The full 2011 ATLAS pp collision data set from the LHC (4.7 fb(-1)) is used to search for t(t)over-bar events produced in association with jets, in which one of the W bosons from the top quarks decays leptonically and the other decays hadronically. The data are consistent with the Standard Model expectation, and a new particle with mass below 430 Gev for both W' boson and color triplet models is excluded at 95% confidence level, assuming unit right-handed coupling.

Abstract: A search for squarks and gluinos in final states containing jets, missing transverse momentum and no high-p(T) electrons or muons is presented. The data represent the complete sample recorded in 2011 by the ATLAS experiment in 7 TeV proton-proton collisions at the Large Hadron Collider, with a total integrated luminosity of 4.7 fb(-1). No excess above the Standard Model background expectation is observed. Gluino masses below 860 GeV and squark masses below 1320 GeV are excluded at the 95% confidence level in simplified models containing only squarks of the first two generations, a gluino octet and a massless neutralino, for squark or gluino masses below 2 TeV, respectively. Squarks and gluinos with equal masses below 1410 GeV are excluded. In minimal supergravity/constrained minimal supersymmetric Standard Model models with tan beta = 10, A(0) = 0 and μ> 0, squarks and gluinos of equal mass are excluded for masses below 1360 GeV. Constraints are also placed on the parameter space of supersymmetric models with compressed spectra. These limits considerably extend the region of supersymmetric parameter space excluded by previous measurements with the ATLAS detector.