The aerogel threshold Cherenkov detector for the high momentum spectrometer in Hall C at Jefferson Lab

We describe a new aerogel threshold Cherenkov detector installed in the HMS spectrometer in Hall C at Jefferson Lab. The Hall C experimental program in 2003 required an improved particle identification system for better identification of pi/K/p, which was achieved by installing an additional threshold Cherenkov counter. Two types of aerogel with n = 1.030 and n = 1.015 allow one to reach similar to 10(-3) proton and 10(-2) kaon rejection in the 1-5 GeV/c momentum range with pion detection efficiency better than 99% (97%). The detector response shows no significant position dependence due to a diffuse light collection technique. The diffusion box was equipped with 16 Photonis XP4572 photo multiplier tubes (PMTs). The mean number of photo-electrons in saturation was similar to 16 and similar to 8, respectively. This allows even for separation of slower particles slightly above threshold. (c) 2005 Elsevier B.V. All rights reserved.