Performance of the NOMAD-STAR detector

The NOMAD-STAR detector is a silicon vertex 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 1.14m^2. About 11,500 nu_mu 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 nu_mu (nu_e)<-> nu_tau oscillations depends on the observation of the tau candidates by the experimental signature of a large impact parameter, in the case of the one prong decay of the tau, 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 peformance achieved with it. PACS : 13.15.+g; 14.60.Lm; 14.60.Pq; 29.40Gx; 29.40.Wk Keywords Neutrino physics; Silicon microstrip detectors