First beam exposures of a scintillating fibre 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 μm × 500 μm 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 μm 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 μm standard deviation σ. The centre-of-gravity precision ϵ=σ/N (N = number of hits) amounts to 15 μm and the angular precision of the tracks peaks at 8 mrad.