The ATLAS level-1 barrel muon trigger performances

The level-1 muon trigger of ATLAS is expected to select events with high transverse momentum muons and associate them the correct bunch-crossing. For these purposes, dedicated fast detectors provide coarse measurement of the muon transverse momentum and high efficiency in its discrimination, giving also tracking measurements in two orthogonal views. In the barrel region (|eta|<1) it makes use of resistive plate chambers (RPCs) as active detectors. The trigger and readout chain is based on custom ASIC chips, which perform both the time and spatial coincidence with programmable roads and signal time shaping, and the readout, with a time resolution of 1/8 of a bunch crossing. A calibration procedure will allow to align signals in time and improve the background rejection of the system. The trigger system performances have been studied, testing multiple trigger configurations, on a cosmics test-stand using a full trigger tower of the ATLAS muon barrel spectrometer and the complete ATLAS trigger chain