Time Calibration of the LHCb Muon System

The muon system of the LHCb experiment at the LHC consists of about 125,000 readout channels based on multi wire proportional chambers (MWPC) and three stages gas electron multipliers (3GEM). The detectors are mounted over 5 walls having in average 10 m of height and placed about 1 m one after the other, named as M1 to M5. The system plays a basic role in the first LHCb trigger level (hardware level). A nominal trigger operation requires 95% efficiency in muon tracks detection. In this respect, it is necessary to reach a time alignment of the system channels at the level of about 2-3 ns. Moreover, this level of synchronization must be monitored to be kept against possible fluctuations due to possible changes in the operating conditions of the detectors. We describe the custom instrumentation implemented at system level for time calibration, the strategy adopted, the procedure to be followed both for system alignment and monitoring, the control program realized for this purpose. First results obtained on a complete system chain are also illustrated.