Measurement of K L 0 flux at the J-PARC neutral-kaon beam line

Abstract We describe the K L 0 flux measurements performed at the J-PARC neutral-kaon beam line. This beam line was constructed for an experiment aiming to observe the CP-violating rare decay K L 0 → π 0 ν ν ¯ . The primary proton energy was 30 GeV and the K L 0 production angle was 16°. Prior to the physics run, the K L 0 flux and spectrum were measured by counting K L 0 → π + π − π 0 decays with a simple setup, which was composed of an electromagnetic calorimeter and a hodoscope system. Results from these measurements are presented and compared with various hadron-interaction simulations.