Performances of a prototype for the ALICE muon trigger at LHC

The ALICE detector at the LHC will be equipped with a forward spectrometer to identify heavy quarkonium states from their decay into muons. The trigger system of the spectrometer consists of four RPC planes, front-end and fast-decision electronics. It is designed to reconstruct muon tracks in a large background environment and to provide a fast trigger signal to the spectrometer. We present results from tests of a trigger prototype that have been carried out with the muon beam of the CERN/SPS at the Gamma Irradiation Facility. The track reconstruction efficiency as well as the robustness of the system to background are discussed.