Data reconstruction with the LHCb VELO: Hit processing, tracking, vertexing and luminosity monitoring

The LHCb experiment is dedicated to performing a detailed study of CP symmetry violation and rare decays of B and D mesons. In order to reach these physics goals the LHCb spectrometer must provide excellent vertexing and tracking performance both off-line and on-line in the trigger. The LHCb VELO (VErtex LOcator) is the silicon microstrip detector which surrounds the collision point and hence is critical to these aims. Its hit processing and zero suppression is performed in a series of algorithms implemented on FPGAs. The tuning of the parameters of these algorithms is performed using a bit-perfect emulation of these algorithms integrated in to the full off-line software of the experiment. Tracking and vertexing is then performed using the clusters produced. These algorithms are described and the results for primary and secondary vertex resolutions are given. Finally, a novel technique for measuring the absolute luminosity using gas injection in the VELO is described.