First operation of a hybrid photon detector prototype with electrostatic cross-focussing and integrated silicon pixel readout

We report on the first operation of a hybrid photon detector prototype with integrated silicon pixel readout for the ring imaging Cherenkov detectors of the LHCb experiment. The photon detector is based on a cross-focussed im age intensifier tube geometry where the image is de-magnified by a factor o f 4. The anode consists of a silicon pixel array, bump-bonded to a binary r eadout chip with matching pixel electronics. The prototype has been charact erized using a low-intensity light-emitting diode operated in pulsed mode. Its performance in terms of single-photoelectron detection efficiency and i maging properties is presented. A model of photoelectron detection is propo sed, and is shown to be in good agreement with the experimental data. It in cludes an estimate of the charge signal generated in the silicon detector, and the combined effects of the comparator threshold spread of the pixel re adout chip, charge sharing at the pixel boundaries and back-scattering of t he photoelectrons at the silicon detector surface. (C) 2000 Elsevier Scienc e B.V. All rights reserved.