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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.

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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. IntroductionIn a collider event the missing transverse momentum is defined as the momentum imbalance in the plane transverse to the beam axis, where momentum conservation is expected. Such an imbalance may signal the presence of unseen particles, such as neutrinos or stable, weakly-interacting supersymmetric (SUSY) particles. The vector momentum imbalance in the transverse plane is obtained from the negative vector sum of the momenta of all particles detected in a pp collision and is denoted as missing transverse momentum, E miss T . The symbol E miss T is used for its magnitude. A precise measurement of the missing transverse momentum, E miss T , is essential for physics at the LHC. A large E miss T is a key signature for searches for new physics processes such as SUSY and extra dimensions. The measurement of E miss T also has a direct impact on the quality of a number of measurements of Standard Model (SM) physics, such as the reconstruction of the top-quark mass in tt events. This paper describes an optimized reconstruction and calibration of E miss T developed by the ATLAS Collaboration. The performance achieved represents a significant improvement compared to earlier results [2] presented by ATLAS. The optimal reconstruction of E miss T in the ATLAS detector is complex and validation with data, in terms of resolution, scale and tails, is essential. A number of data samples encompassing a variety of event topologies are used. Specifically, the event samples used to assess the quality of the E miss T reconstruction are: minimum bias events, events where jets at high transverse momentum are produced via strong interactions described by Quantum Chromodynamics (QCD) and events with leptonically decaying W and Z bosons. This allows the full exploitation of the detector capability in the reconstruction and calibration of different physics objects and optimization of the E miss T calculation. Moreover, in events with W → ν , where is an electron or muon, the E miss T performance can be studied in events where genuine E miss T is present due to the neutrino, thus allowing a validation of the E miss T scale. In simulated events, the genuine E miss T , E miss,True T ...

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