Triggering on low-$p_T$ muons and di-muons for $B$-physics

Muon pairs from jpsi decay are a clear signature of $b$ hadrons. As a large fraction of $b$ hadrons are produced at low-$p_T$, a low rate, efficient di-muon trigger for low-$p_T$ muons and a good understanding of the trigger efficiency are essential. Di-muon final states will also play a key role in calibration, alignment and determination of the trigger efficiencies. The performance of the level-2 dimuon trigger algorithms is discussed, together with a method for reducing backgrounds from decays-in-flight. A strategy for calculating the single muon and di-muon trigger efficiencies at level-1 and level-2 using jpsi from the data themselves is presented.