Performance of the NOMAD-STAR detector

The NOMAD-STAR detector is a silicon vertex detector installed in the NOMAD spectrometer at the CERN SPS neutrino beam. It consists of four layers of a passive boron carbide target with a total mass of 45 kg and five layers of 600 single-sided silicon microstrip detectors covering a total area of 1.14 m<sup>2</sup>. About 11,500 ν<sub>μ</sub> charged current interactions were reconstructed in the fiducial volume of NOMAD-STAR from the neutrino run in 1998. The potential use of silicon detectors for ν<sub>μ</sub>(ν<sub>e</sub>) lt - gt ν<sub>τ</sub> oscillations depends on the observation of the τ candidates by the experimental signature of a large impact parameter, in the case of the one prong decay of the τ, or a double vertex, in the case of the three prong decay. The main aim of NOMAD-STAR is to measure the impact parameter and vertex distributions of charged current interactions, which constitute the main backgrounds for the oscillation signals, to understand the significance of a potential signal in a future experiment. The present paper describes the experience gained in the operation of this silicon vertex detector, and the performance achieved with it