Measurement of the ATLAS di-muon trigger efficiency in proton-proton collisions at 7 TeV

The B physics program of the ATLAS experiment includes the study of the production cross sections, the searches for rare b decays signatures which are sensitive to new physics at the TeV energy scale and the measurements of CP violation effects in B-events, such as Bs0 → J/psi phi and Bd → J /psi Ks. The key to the detection of these B signals in ATLAS is to achieve a high trigger efficiency for low-pT di-muons events, while keeping an acceptable trigger rate. Atlas developed two separates approaches for triggering on di-muons events from a resonance such as a J/psi and Upsilon. The first approach is to start from a di-muons trigger selected by the Level-1 trigger while the second is based on dedicated Level-2 algorithm. The performance of di-muons trigger has been studied using collision data at sqrt{s} =7TeV. Results are compared to MonteCarlo predictions.