Performance of a 4-7GeV/c Kaon Identification System in KEK-PS E248

A kaon identification system with momentum range of 4-7GeV/c was used in KEK-PS E248 experiment. The system consisted of two Cherenkov counters. The radiator of the first counter was silica aerogel with the refractive index of 1.007. The counter had six stages and it was used for K/p identification. The radiator of the second counter was SF₆ gas (n= 1.0007). The second counter had two stages and it was used for pi/K identification. Performance of two counters was estimated with using the pions and protons, identified by a TOF system. As for the first counter, typical efficiency of each stage was 49.2% for pions and a typical fake rate of proton was 5%. In case that the number of hit stages ges4, 99.8% of protons were rejected and 50% of pions and kaons were selected. As for the second counter, typical efficiency of each stage was 97.9% for high momentum (>5GeV/c) pions and a typical fake rate of proton was 3%. In case that both stages were no hit, 98.7% of pions were rejected and 97.9% of high momentum kaons and protons were selected. The total system gave rejection efficiency of 98.7% for pions and protons, and 31.5% of kaons were selected.