The LHCb trigger and data acquisition system

• Published in: IEEE transactions on nuclear science 2000-04, Vol.47 (2), p.86-90
• Main Authors: Dufey, J.-P., Frank, M., Harris, F., Harvey, J., Jost, B., Mato, P., Mueller, E.
• Format: Article
• Language: English
• Subjects: Accelerators; Bandwidth; Computer programs; Control systems; Data acquisition; Detectors; Discrete event simulation; Farms; Hardware; Large Hadron Collider; Networks; Physics; Protocol (computers); Protocols; Simulation; Software; Traffic control
• ISSN: 0018-9499; 1558-1578
• DOI: 10.1109/23.846123

The LHCb experiment is the most recently approved of the 4 experiments under construction at CERNs 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 Data Acquisition (DAQ) system will have to cope with an average trigger rate of /spl sim/40 kHz, after two levels of hardware triggers, and an average event size of /spl sim/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 the 40 kHz to /spl sim/100 Hz of events written to permanent storage. In this paper we outline the general architecture of the Trigger and DAQ system and the readout protocols we plan to implement. First results of simulations of the behavior of the event-building network implementations under the expected traffic patterns are presented.