The B physics programme of the ATLAS experiment includes measurements of production cross sections, searches for rare B-decay signatures which are sensitive to new physics at the TeV energy scale and studies of CP violation effects in B-events, such as B_s^0→ J/ψϕ and B_d^0→ J/ψ 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, whilst keeping an acceptable trigger rate. ATLAS developed two separate approaches for

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... ering on di-muon events from resonances such as J/ψ and Upsilon (Υ). The first approach is to start from a di-muon trigger selected at Level-1 while the second is based on dedicated Level-2 algorithms. The performance for these triggers has been studied using collision data at √(s)=7 TeV collected in 2011.