A Measurement of the ATLAS Di-Muon Trigger Efficiency in Proton-Proton Collisions at = 7 TeV

The B physics programme of the ATLAS experiment includes the study of the production cross sections, the searches for rare b decay signatures which are sensitive to new physics at the TeV energy scale and the measurements of CP violation effects in B-events, such as B_s0→J /ψ φ and B_d0→J /ψ K_s0 . The key to the detection of these B signals in ATLAS is to achieve a high trigger efficiency for low-pT di-muon events, keeping an acceptable trigger rate. ATLAS developed two separates approaches for triggering on di-muon events from a resonance such as J/ψ and ϒ. The first approach is to start from a di-muon trigger selected by the Level-1 trigger while the second is based on dedicated Level-2 algorithm. The performance of di-muon trigger has been studied using collision data at sqrt(s)= 7 TeV. Results are shown and compared to MonteCarlo predictions.