Update on the performance of the HERA-B Vertex Detector System

The HERA-B Vertex Detector System (VDS) is a Roman Pot system integrated into the proton ring of the HERA accelerator at DESY and serves as an independent part of the tracking system of the HERA-B forward spectrometer. The performance of the VDS meets the design specification. It is based on double-sided silicon micro-strip detectors which are operated as close as 1 cm to the beam and are thus exposed to extremely high and inhomogeneous radiation levels. At the design luminosity the peak irradiation is around 3 x 10(14) minimum ionizing particles per cm(2) per year. Test measurements have shown adequate radiation tolerance on the required time scale of I year. New long-term studies presented here indicate that on periods longer than I year charge collection efficiencies might drop. (C) 2003 Elsevier B.V. All rights reserved