A Measurement of the ATLAS Di-Muon Trigger Efficiency in Proton-Proton Collision at $\sqrt{s} = 7$TeV

The B physics program 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 measurement of CP violation effects in B-events, such as $B_{s}^{0}ightarrow J/psi phi$ and $B_{d}^{0} ightarrow J/psi K_{s}^{0}$. The key to the detection of these B signals in ATLAS is to achieve a high trigger efficiency for low-$p_{T}$ di-muon events, keeping an acceptable trigger rate. ATLAS developed two separate approaches for triggering on di-muon events from resonances such as a $J/psi$ and Upsilon ($Upsilon$). The first approach is to start from a di-muon trigger selected by the Level-1 trigger while the second in based on the dedicated Level-2 algorithm. The performance for di-muon trigger has beed studied using collision data at $sqrt{s}=7$ TeV collected in 2011.