The extended OPAL silicon strip microvertex detector

Abstract The OPAL experiment at the CERN LEP collider recently increased the geometrical acceptance of its silicon microvertex detector. The azimuthal coverage is improved by adding one pair of detectormodules to each of the two layers, while the polar angle coverage is extended by adding new detectormodules in line with the existing ones. This improves the efficiency for high quality tracking in OPAL and in particular for b quark tagging in Higgs bosonsearches. A description of the detectoris given, with emphasis on new or modified elements with respect to the earlier version. Results on the performance of the new detectorare presented.