The argus time-of-flight system

Abstract The time-of-flight system of the ARGUS detector at the DORIS e + e − storage ring consists of 64 barrel scintillation counters covering 75% of 4π, and 2 × 48 end cap counters, covering 17% of 4π. The barrel counters are viewed by two phototubes each, while the end cap counters have one tube only. The time-of-flight system serves as a part of the fast trigger and identifies charged particles. The time resolution achieved during the first year of ARGUS operation is 210 ps for Bhabhas (which are used for the off-line monitoring of the system), and 220 ps for hadrons, both in barrel and end cap counters. This converts into a three standard deviation mass separation up to 700 MeV/ c between pions and kaons and 1200 MeV/ c between kaons and protons. Electrons can be separated from heavier particles up to 230 MeV/ c .