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This paper presents a search for the t-channel exchange of an R-parity violating scalar top quark ( \(\tilde{t}\) ) in the e\(^±\) μ\(^∓\) continuum using 2.1 fb\(^{−1}\) of data collected by the ATLAS detector in √s=7 TeV pp collisions at the Large Hadron Collider. Data are found to be consistent with the expectation from the Standard Model backgrounds. Limits on R-parity-violating couplings at 95 % C.L. are calculated as a function of the scalar top mass (m\(_\tilde{t}\)). The upper limits on the production cross section for pp→eμX, through the t-channel exchange of a scalar top quark, ranges from 170 fb for m\(_\tilde{t}\)=95 GeV to 30 fb for m\(_\tilde{t}\)=1000 GeV.
This paper describes an analysis of the angular distribution of W→eν and W→μν decays, using data from pp collisions at s√=7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb\(^{−1}\). Using the decay lepton transverse momentum and the missing transverse momentum, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f\(_0\), f\(_L\) and f\(_R\) over two ranges of W transverse momentum (p\(^W_T\)):35<p\(^W_T\)<50 GeV and p\(^W_T\)>50 GeV. Good agreement is found with theoretical predictions. For p\(^W_T\)>50 GeV, the values of f\(_0\) and f\(_L\)−f\(_R\), averaged over charge and lepton flavour, are measured to be: f\(_0\)=0.127±0.030±0.108 and f\(_L\)−f\(_R\)=0.252±0.017±0.030, where the first uncertainties are statistical, and the second include all systematic effects.
The measurement of missing transverse momentum in the ATLAS detector, described in this paper, makes use of the full event reconstruction and a calibration based on reconstructed physics objects. The performance of the missing transverse momentum reconstruction is evaluated using data collected in pp collisions at a centre-of-mass energy of 7 TeV in 2010. Minimum bias events and events with jets of hadrons are used from data samples corresponding to an integrated luminosity of about 0.3 nb\(^{−1}\) and 600 nb\(^{−1}\) respectively, together with events containing a Z boson decaying to two leptons (electrons or muons) or a W boson decaying to a lepton (electron or muon) and a neutrino, from a data sample corresponding to an integrated luminosity of about 36 pb\(^{−1}\). An estimate of the systematic uncertainty on the missing transverse momentum scale is presented
Detailed measurements of the electron performance of the ATLAS detector at the LHC are reported, using decays of the Z, W and J/ψ particles. Data collected in 2010 at s√=7 TeV are used, corresponding to an integrated luminosity of almost 40 pb\(^{−1}\). The inter-alignment of the inner detector and the electromagnetic calorimeter, the determination of the electron energy scale and resolution, and the performance in terms of response uniformity and linearity are discussed. The electron identification, reconstruction and trigger efficiencies, as well as the charge misidentification probability, are also presented.