A
 measurement 
of
 the
 ATLAS
 
di‐muons
 trigger 
efficiency 
in
 proton‐proton
 collisions
 at
 sqrt(s) =
7
TeV.


The B physics programme 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/ψφ and Bd0→J/ψKs0. The key to the detection of these B signals in ATLAS is to achieve a high trigger efficiency for low-pT di-muons events, keeping an acceptable trigger rate. Atlas developed two separates approaches for triggering on di-muons events from a resonance such as J/ψ and Υ. 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) = 7 TeV in 2011 data. Results are shown and compared to MonteCarlo predictions.