The LHCb track trigger

LHC-B, the proposed B-physics experiment at the LHC collider at CERN, has to face a huge background from minimum bias events in comparison to the production cross section for hadrons containing b quarks. This note describes the LHC-B level 1 track trigger, which is supposed to find charged tracks within 256_s in the angular range between 10 and 300 mrad with respect to the beam pipe, i.e. in an environment of extremely high particle density. A high track finding efficiency is obtained by using a simplified Kalman filter algorithm. The number of minimum bias events is reduced by a factor 3 based on the pattern recognition alone, and an additional factor 2 to 3 when a transverse momentum cut on single tracks is applied. The hardware implementation of the algorithm is discussed1