  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 $B_{s}^{0}\rightarrow J/\psi \phi$ and
$B_{d}^{0}\rightarrow J/\psi K_{s}^{0}$. 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, whilst keeping an acceptable trigger rate. ATLAS developed two
separate approaches for triggering on di-muon events from resonances such as
$J/\psi$ and Upsilon ($\Upsilon$). 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 $\sqrt{s}=7$ TeV collected in 2011.
