FIRST BEAM EXPOSURES OF A SCINTILLATING-FIBER TRACKER READ-OUT BY AN ISPA-TUBE

The ISPA (imaging silicon pixel array)-tube is a new position-sensitive photon detector. It represents a vacuum-sealed cylinder of 45 mm length and 35 mm diameter, which encloses a photocathode confronted at 30 mm distance by a silicon chip containing 1024 pixels of 75 mu m X 500 mu m edges bump bonded to their individual front-end electronics. The photoelectrons were accelerated by 20 kV potential difference towards this anode chip. Track patterns, emitted from a fibre tracker (composed of 60 mu m diameter scintillating fibres) and exposed to 120 GeV/c negative pions, were read out with this recently developed device. The Gaussian of the track residuals indicates 42 mu m standard deviation a. The centre-of-gravity precision epsilon = sigma/root N (N = number of hits) amounts to 15 mu m and the angular precision of the tracks peaks at 8 mrad.