LHCb Global Timing and Monitoring of the LHC Filling Scheme

The LHC experiments rely on a proper and stable timing for the sampling of the detector signals and for the synchronization of the readout system. The LHC timing is distributed and received at the experiments by a system which is common to all experiments. The control and monitoring of the reception, and the integration into the overall experiment control system has been developed individually by each experiment. In addition, the experiments have developed methods to monitor the LHC bunch timing based on beam pickups in order to assure the required stability of the experiment clock with respect to the bunch arrival times, and the position of the interaction region. In LHCb, this system also allows monitoring the individual bunch intensities and the filling scheme which are vital to the special random triggers used for both the online and offline determination of total luminosity and luminosity per bunch. The timing resolution is such that it also allows detecting ghost and satellite bunches down to 2*109 protons in any 2.5ns RF bucket. The bunch monitoring system developed by LHCb is also used by the ALICE experiment. This document describes the LHCb global timing, the central distribution, and the control and monitoring as well as the consequences for the operational procedures. It also presents the experience and results during the beam commissioning, during which it provided valuable information to the LHC, and the first months of LHCb data taking.