Design of the neutral K0L beamline for the KOTO experiment

The J-PARC E14 KOTO experiment aims at the first observation of the K L 0 → π 0 ν ν ¯ decay. This experiment requires a well-collimated neutral beam with the small amount of halo neutrons. Collimation lines and beamline components in the beamline have been optimized to suppress halo neutrons by utilizing the GEANT-3 Monte-Carlo simulation package. We have achieved the design with sharp cross-sectional profiles of the beam and the halo-to-core neutron flux ratio of 10−5 level.