An high efficiency photon veto detector for a experiment

The P326 project aims to measure 40 events/year of the very rare decay K + → π + ν ν ¯ at the CERN SPS. This poses unprecedented requirements in terms of the tracking and identification of charged particles, and also calls for excellent photon rejection to fight the abundant π + π 0 background. A full angular coverage up to 50 mrad for photon detection will be provided by the NA48 liquid-krypton calorimeter complemented by a set of 13 photon counter rings along the decay tunnel at large angles, and by small angle calorimeters.