DEVELOPMENT OF A LARGE-AREA AEROGEL CHERENKOV COUNTER ONBOARD BESS

This paper describes the development of a threshold-type aerogel Chere nkov counter with a large sensitive area of 0.6 m(2) to be carried onb oard the BESS rigidity spectrometer to detect cosmic-my antiprotons. T he design incorporates a large diffusion box containing 46 finemesh ph otomultipliers, with special attention being paid to achieving good pe rformance under a magnetic field and providing sufficient endurance wh ile minimizing material usage. The refractive index of the aerogel was chosen to be 1.03. By utilizing the muons and protons accumulated dur ing the cosmic-ray measurements at sea level, a rejection factor of 10 (4) was obtained against muons with beta approximate to 1, while keepi ng 97% efficiency for protons below the threshold. (C) 1998 Elsevier S cience B.V. All rights reserved.