Performance study of the level-1 di-muon trigger

An event with two muons in the final state is a distinctive signal and can be triggered efficiently with the use of the level-1 di-muon trigger. Nevertheless triggering is still an issue if these muon tracks are fairly soft and fake di-muon triggers originating from muons that traverse more than one region of the trigger chambers increase the trigger rate. It is important to provide an acceptable trigger rate, while keeping high trigger efficiency to study low-pt $B$-physics such as rare $B$ hadron decays or CP violation in the $B$-events, especially in a multi-purpose experiment like ATLAS. In this note, the level-1 di-muon trigger and its expected performance are described.