Time-of-Propagation Counter for the LEPS

We have tested a time-of-propagation (TOP) counter, which is a ring-image Cherenkov counter utilizing the position and propagation time of the Cherenkov light produced by particles moving in a quartz radiator. Position-sensitive photomultipliers (PMTs) are attached to the end of the quartz bar to detect the produced Cherenkov-ring image. The velocity of the charged particle was determined by comparing the time-of-propagation spectra of the Cherenkov light with the results of Monte Carlo simulation. From analysis of the test experiment using the 1.22-GeV/c electron beam at SPring-8, we determined the velocity of the electron beam to be 1.001 with a resolution of 0.002. On the basis of this study, we suggest a full setup for the detector for separating pions and kaons in the momentum region from 1.5 to 2.0 GeV/c for a beam angle of less than 6°, by more than four standard deviations.