Performance of an aerogel threshold particle identification detector readout by hybrid photon detectors

This paper describes an aerogel threshold particle identification detector developed for use in BABAR, the experiment to be run at the asymmetric e/sup +/e/sup -/ B-factory PEP-II under construction at the Stanford Linear Accelerator Center (SLAC). Results of extensive tests performed at the CERN PS indicate that this detector is capable of separating pions from below-threshold particles in a wide momentum range. The detector is read by a new version of a hybrid photon detector (HPD). The HPD has been chosen because of its excellent behavior in high magnetic fields, where it can be successfully exploited to preserve the required particle identification (PID) performance.