Performance evaluation of an electron veto counter with silica aerogel of n ≪ 1.003

In the LEPS (Laser Electron Photon at Spring-8) experiment [1], we use a photon beam which is generated through laser induced backward Compton scattering with the circulating 8GeV electron beam in the synchrotron radiation ring. The energy range of the photons is between about 1.5 GeV and 3.0 GeV, and the typical intensity is 106 photons/sec.