R&D work on a liquid-xenon photon detector for the μ→eγ experiment at PSI

We are developing a new type of photon detector for an experiment to search for muons decaying into positrons and gamma rays. The detector utilizes liquid xenon as a scintillation material. The scintillation light emitted in liquid xenon is directly observed by photomultipliers (PMTs) located in the liquid without the use of a transmission window. In order to study the detector response, we have constructed a prototype with an active volume of about 70 l surrounded by 228 PMTs. For studying the detector response we conducted electron and gamma beam tests together with detector calibration using alpha sources and cosmic-ray events. In this article we describe preliminary results obtained in these tests.