Studies on wrapping materials and light collection geometries in plastic scintillators

The KOPIO experiment at BNL was intended to measure the branching ratio of the ultra-rare (SM prediction about 3 × 10 - 11 ) decay K 0 → π 0 ν ν ¯ with a precision of O ( 10 % ) . efficient veto systems are required to keep background from kaon decays with additional photons or charged particles under control. The planned charged particle veto system consists of about 40 m 2 organic scintillator operated in vacuum and aims at efficiencies > 99.99 % . To reach the required 50 keV detection threshold a very high light collection efficiency has to be achieved. We here report on our extensive studies of light guide geometries and different wrapping materials used to maximize light collection.