Development of silica aerogel Cherenkov counter with n = 1.003 for electron veto

We are developing a new Cherenkov counter using a silica aerogel for the LEPS (laser electron photon at SPring-8) experiment in order to veto background positron-electron events. The veto counter is important to investigate more interesting hadronic events. We are using aerogels with a refractive index (n) of 1.03 or 1.008 in the present counter. In this case, not only electrons but also pions are removed. For the research of pion events, it is necessary for aerogel Cherenkov counter (AC) not to remove pions. We focus on aerogels with n = 1.003 as a solution to this problem. In the current study, we propose a new AC possessing enough detection efficiency. By using this AC, only positron-electrons would be removed.