Measurement of KL0 flux at the J-PARC neutral-kaon beam line

We describe the KL0 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 KL0→π0νν¯. The primary proton energy was 30 GeV and the KL0 production angle was 16°. Prior to the physics run, the KL0 flux and spectrum were measured by counting KL0→π+π−π0 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.