The LHCb DAQ system

The LHCb experiment is the most recently approved of the 4 experiments under construction at CERN´s LHC accelerator. It is a special purpose experiment designed to precisely measure the CP violation parameters in the B-B system. Triggering poses special problems since the interesting events containing B-mesons are immersed in a large background of inelastic p-p reactions. We therefore decided to implement a 4 level triggering scheme. The LHCb DAQ system will have to cope with an average trigger rate of ~40 kHz, after two levels of hardware triggers, and an average event size of ~150 kB. Thus an event-building network which can sustain an average bandwidth of 6 GB/s is required. A powerful software trigger farm will have to be installed to reduce the rate from the 40 kHz to ~200 Hz of events written to permanent-storage. In this paper we will concentrate on the networking aspects of the LHCb data acquisition and the control system