E. Borsato

Abstract

The principle of operation of a newly developed proximity focused Hybrid Photon Detector is described. The HPD characteristics, performance and calibration are reported. Results from beam tests of aerogel threshold counters read-out by HPD and the particle identification performance are presented. 1 The Hybrid Photon Detector The operating principle of the proximity focused Hybrid Photon Detector (HPD) is shown in figure 1. Light striking on a 2 mm thick quartz window hits an S20 UV photocathode that features a high quantum efficiency response peaked in the UV region (figure 2). Photoelectrons are accelerated by a uniform electric field and penetrate in the depleted region of a 300 ¯m thick 1 inch diameter silicon diode operated in reverse-bias mode. The kinetic energy is converted into a charge pulse picked up at the diode contacts. The gain is about 3300 at the operating high voltage of 15 kV . The electric output signal is subsequently amplified and conveniently shaped to be measur..