Performance of the ATLAS transverse energy triggers with initial LHC runs at sqrt(s) = 7 TeV

The performance of the ATLAS triggers based on the vector and scalar sums of the transverse energies is shown for LHC proton-proton collision events at sqrt(s) = 7 TeV recorded from 19 August to 29 October 2010. In the data set considered here, the mean number of collisions per bunch crossing ranged from 0.6 to 3.8 and the instantaneous luminosity ranged from 0.3 to 21 x 1e31 cm-2 s-1. Comparisons between data taken at different luminosities, trigger and offline measurements, and data and simulations show that the trigger behaved as expected. Because the shape of the energy spectra depend on the number of collisions in each bunch crossing, it was necessary to adjust energy thresholds in order to maintain acceptable trigger rates. The trigger nonetheless proved to be robust and reliable enough to be used in selecting events for physics analysis.