A di-muon selection for the second level trigger in the ATLAS detector

The B production cross section at the LHC is very high, but it is just a small fraction of the total inelastic cross section (0.7%), therefore the trigger for B physics is required to be very selective. The output rate of the first level trigger is expected to contain 20 KHz of events with at least one energetic muon with p_T above 6 GeV. Most of these events are from K and pi decays, and only 4 KHz are b events. At the second level trigger (level 2) this rate of events must be reduced to 2-10 KHz. Currently this goal is achieved by confirming a muon in the inner detector in addition to confirming it in the muon spectrometer. This selection criterion removes K and pi decays, but many interesting b events are likely to be filtered out as well. Acceptable first level trigger (level 1) rates in ATLAS have been reduced due to "staging" of high level trigger processing power. Envisioned trigger menus now include 2 low p_T mu or one higher p_T mu. This would reduce the number of available b-physics events. Algorithms are developed for recovery of the most promising b events at level 2. We developed an algorithm which achieves high efficiency for the "gold" channels (J/Psi) at level 2 using the identification of relatively low p_T muons that decay from J/Psi. Physics and time performance of the algorithm will be presented here.