Study on GASTOF – A 10 ps resolution timing detector

Abstract

GASTOF (Gas Time Of Flight) is a type of fast-time detector affiliated to the HPS (High Precision Spectrometer) project which is a forward physics collaborator within CMS. It is a picosecond time resolution Cherenkov gas detector using very fast single anode micro-channel plate photomultiplier (Hamamatsu R3809U-50 or Photek 210) as a photon detector. We firstly measured characteristics of these two types of MCP-PMTs by a fast laser pulse in lab. Then two GASTOF detectors both equipped with a Hamamatsu R3809U-50 tube were studied in a beam test at CERN. According to the analysis of beam test data, the average number of photoelectrons (phe) was 2.0 for both phototubes. By making a cut on the number of photoelectrons such that the mean phe was 3.6 in one phototube and 3.2 in another, we obtained a time resolution of σ~11.7 picosecond (ps) and σ~8.2ps.