The data acquisition system for the CMS experiment at the LHC

The trigger and data acquisition systems will play a key role in experiments at the Large Hadron Collider (LHC) currently under construction at CERN. At the LHC, with a beam-crossing frequency of 40 MHz, and a design luminosity of 10/sup 34/ cm/sup -2/ s/sup -1/, an average of 20 inelastic pp events will be produced per crossing. The CMS detector, with more than 10/sup 8/ electronics channels, will produce ~1 MB of zero-suppressed data per crossing, so that both the collision and the overall data rates are many orders of magnitude larger than the current goals of storing events at a rate of O(100)Hz at data rates of O(100) MB/s respectively. The CMS trigger and data acquisition system is designed to analyse the detector information at the full crossing rate and to select a maximum of 100 Hz of events to be stored for offline analysis. (10 refs).