B Physics Triggers at Cms 2 the Cms Trigger and Data Acquisi- Tion 3 the Level-1 Triggers

The CMS detector is mainly designed to investigate hard events. Only few Level-1 Trigger conditions are suitable to select soft B-meson decays. The B-physics potential of CMS depends strongly on a selection strategy at High-Level Trigger. The selection algorithms for some benchmark B-decay channels that allow CMS to perform competitive B-physics program are presented. 1 Introduction The CMS detector [ 1] is designed and optimized for discovery physics, in particular the observation of the Higgs boson(s) and the investigation of supersymme-try or other physics beyond the standard model. Nevertheless , B physics may be an interesting subject, especially during the low luminosity (2×10 33 cm −2 s −1) phase. The study presented in this note has been done for this phase. The B-physics potential of the CMS detector depends on many factors but mostly on the trigger conditions that will be used to collect events for further offline analysis. While the main Level-1 triggers are almost defined, the High-Level Triggers (HLT) are currently under discussion and investigation. In this note, possible HLT selection algorithms for several B decay channels of interest are presented. The CMS Trigger and Data Acquisition System (Tri-DAS) is designed to inspect the detector information at the full beam crossing rate of 40 MHz and to select events at a maximum rate of O(10 2) Hz for archiving and later offline analysis. The required rejection power of O(10 5) is too large to be archived in a single processing step. For this reason, the full selection task is split in two steps. The first step (Level-1 Trigger) is designed to reduce the rate of events accepted for further processing to less than 100 kHz. The time available for actually processing the data is about 1µs. Therefore the Level-1 Trigger can only process data from a subset of CMS sub-detectors, the calorimeters and muon chambers. Moreover, this data do not represent the full information recorded in the CMS front-end electronics, but only a coarse-granularity and lower-resolution set. The second step (High-Level Trigger) * On leave from ITEP, Moscow, Russia is designed to reduce the maximum Level-1 accept rate of 100 kHz to a final output rate of 100 Hz. The event selection at this stage takes advantage of the enhanced granularity and resolution available and makes use of information from tracking detectors. The HLT selection algorithms are actually almost as sophisticated as those used in the offline reconstruction …