KOTO II at J-PARC : toward measurement of the branching ratio of KL→π0νν¯
H. Nanjo
Abstract
Abstract The KOTO II experiment at J-PARC is a next-generation experiment that is under design aiming at the measurement of the branching ratio of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>K</mml:mi> <mml:mi>L</mml:mi> </mml:msub> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> decay. The KOTO II experiment is planned in the extended Hadron Experimental Facility at J-PARC using the second production target. With the second production target, the K L extraction angle of 5 degrees is chosen instead of 16 degrees in order to obtain a larger K L flux and harder K L momentum spectrum while keeping the same ratio of neutron and K L fluxes. To realize the extraction angle, the KOTO II detector is behind the primary beam dump. The KOTO II detector has a longer decay volume and a larger calorimeter to achieve a larger decay probability and higher acceptance of the K L decay. With the designed beam line and the detector, 40 signal events are expected for the branching ratio of 3×10 −11 with 60 background events in the running period of 3 × 10 7 s, which corresponds to approximately 5- σ discovery of the decay.