A time-of-flight measurement system for the HADES wide-aperture dielectronspectrometer

The HADES spectrometer and a time-of-flight detector based on long-sized (5 0-250 cm) scintillation counters are described, The detector is designed fo r identification of electrons, pions, and protons with moments of 0.1-1.5 G eV/c at a flight distance of 220-250 cm. The operating conditions are analy zed, and the requirements to the detector and counter design are formulated . The design of the counters and their arrangement in the spectrometer are considered. The results of experimental studies of such characteristics of long counters as the light attenuation length in a scintillator and tempora l and spatial resolutions, depending on the location of the point of the pa rticle's hit on the counter, are presented. Analysis of the data has shown that the main factor determining the spatial resolution of long counters is the quality of the polishing of the side faces of the scintillator's, whic h determines the effective (averaged over the scintillator side surfaces) c oefficient of total internal reflection R. It is shown that, for R greater than or equal to 0.99, it is quite possible to achieve temporal and spatial resolutions of 100 ns and 2-3 cm, respectively, for scintillators with a l ength of up to 250 cm and a cross section of 1-20 cm(2), Foreign and Russia n photomultipliers were used in the counters.