Testbeam results on particle identification with aerogel used as RICH radiator

We present the results obtained by exposing samples of silica aerogel of different thickness and optical properties to pion and proton beams with momenta between 6 and 10 GeV/c in the PS testbeam facility at CERN. Two large diameter pad hybrid photodiodes with 2048 channels, produced at CERN, have been used as photon detectors. Separate Cherenkov rings produced by the different particles were reconstructed obtaining pion/proton separation over the whole momentum range. The number of photoelectrons was measured as a function of aerogel thickness and was found to be in agreement with Monte Carlo expectations.