First-year experience with the BaBar silicon vertex tracker

Within its first year of operation, the BaBar Silicon Vertex Tracker (SVT) has accomplished its primary design goal, measuring the z vertex coordinate with sufficient accuracy as to allow the measurement of the time-dependent CP asymmetry in the neutral B-meson system. The SVT consists of five layer s of double-sided. AC-coupled silicon-strip detectors of 300 mum thickness with a readout strip pitch of 50-210 mum and a stereo angle of 90 degrees b etween the strips on the two sides. Detector alignment and performance with respect to spatial resolution and efficiency in the reconstruction of sing le hits are discussed. In the day-to-day operation of the SVT., radiation d amage and protection issues were of primary concern. The SVT is equipped wi th a dedicated system (SVTRAD) for radiation monitoring and protection, usi ng reverse-biased photodiodes. The evolution of the SVTRAD thresholds on th e tolerated radiation level is described. Results on the first-year radiati on exposure as measured with the SVTRAD system and on the so far accumulate d damage are presented. The implications of test-irradiation results and po ssible future PEP-II luminosity upgrades on the radiation limited lifetime of the SVT are discussed. (C) 2001 Elsevier Science B.V. All rights reserve d.