Detailed Performance Study of ATLAS Endcap Muon Trigger with Beam Collision

Since the first p-p collision of the LHC, The Trigger System has been providing level-1 trigger signals of muon candidates with the specified latency to the central trigger system. The timing calibration is a vital issue to identify the bunch crossing number, which contains the high-momentum muon objects. To determine the bunch crossing identification number correctly, the signal delay parameters of all the 320k channels are aligned and the timing for opening the gate is adjusted to the fastest signal according to the result of a clock phase scan with a precision of 1nsec. After the timing calibration and the optimization of trigger conditions, the trigger efficiency is measured as 93.6% at the plateau region using the muon tracks originating from beam collisions. In this paper, we report on detailed studies about trigger efficiencies, optimization of coincidence windows and adjustment of gate timing based on the experience of the data acquisition of several months.