The LHCb front-end electronics and data acquisition system

The LHCb experiment is the most recently approved of the four experiments under construction at CERNʹs LHC accelerator. It is a special purpose experiment designed to precisely measure the CP violation parameters in the B–B̄ system and to study rare B-decays. 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 four-level triggering scheme. The LHCb data acquisition (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 100 kB. Thus, an event-building network which can sustain an average bandwidth of 4 GB/s is required. A powerful software trigger farm will have to be installed to reduce the rate from 40 kHz to 100 Hz of events written for permanent storage. In this paper we will outline the general architectures of the front-end electronics and of the trigger and DAQ system and the readout protocols we plan to implement.