ATLAS trigger for B-physics

The unprecedented rate of bb production at the Large Hadron Collider opens up the possibility to study rare decays including those interesting for CP-violation measurements. The 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 bb quark 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 trigger must be flexible to allow for future evolution, both to study different channels and as luminosity increases. The ATLAS trigger consists of three levels. Level-one is implemented in hardware, whilst the higher levels are based on general-purpose processors. In this paper the ATLAS trigger strategy is described and is illustrated using the following three channels: B/sub d//sup 0/ to pi /sup +/ pi /sup -/ and B decays including the subsequent decays D/sub s//sup -/ to phi (K/sup +/K/sup -/) pi /sup -/ and J/ psi to e/sup +/e/sup $/. (11 refs).