Performance of the trigger detectors of the ALICE muon spectrometer during the first years of data taking at LHC

The trigger system of the ALICE muon spectrometer consists of 4 planes of Resistive Plate Chambers (RPC) for a total of 72 modules covering an area of 140 m². The detectors are read out by means of 21K front-end channels and the signals are processed by fast electronics providing the muon trigger to the experiment. In 2010 and 2011 the muon spectrometer was operational during the whole LHC running period which includes p-p collisions at √s = 7 TeV and 1 month of Pb-Pb collisions at √SNN = 2.76 TeV. The RPCs were operated in avalanche mode in highly-saturated conditions. The detector working parameters, after the setting-up performed during the commissioning with cosmic muons, have been fine-tuned later on using the high statistics of muon tracks from p-p collisions. The behavior of the trigger detectors during the first years of data taking will be presented. In particular, besides a description of the optimization of the RPC running parameters, the stability of the detector performance will be discussed.