Performance of EtMiss reconstruction in first ATLAS data at a center-of-mass energy of 7 TeV

The performance of the missing transverse energy (Etmiss) reconstructed with the ATLAS detector is assessed in proton-proton collisions at a centre-of-mass energy of 7 TeV. We report on results in randomly-triggered events, soft proton proton collisions and collisions with jets at high transverse momentum where Etmiss is expected to be zero. We also report on first Etmiss measurements in events where a W-boson is produced. Particular attention is given to tails in the Etmiss distribution and a measurement of the Etmiss resolution. The performance of the calibration and the individual terms contributing to Etmiss are discussed.