ATLAS B-trigger update

The ATLAS trigger must have very good selectivity in order to reduce the interaction rate by about six orders of magnitude for recording. About one collision in every hundred will produce a bbquark pair. Therefore, in addition to rejecting background from non-bb events, the trigger must have the ability to identify and select those events containing the B-decay channels of specific interest. The ATLAS trigger consists of three levels. Level-1 is implemented in hardware, whilst the higher levels are based on general-purpose processors. The trigger must have the flexibility to change selections both during a beam-coast, as the luminosity falls, and over a longer time-scale as the peak luminosity of the LHC increases. In this paper an update on the ATLAS B-trigger strategy is given. Recent studies have focused on optimising the trigger selection within the finite computing resources that will be available to the trigger. New techniques have been studied, including the use of calorimeter information to minimise the volume of Inner Detector data to be processed. (11 refs) .