KL reconstruction for the Belle experiment at KEK B-factory

We report the K L reconstruction algorithm and its performance for the Belle experiment at KEK B-factory. We select the K L candidates using the dedicated K L detector and electromagnetic calorimeter by detecting the hadron shower caused by K L . Simple cut criteria with K L detector shows the detection efficiency over 50% for the K L momentum above 1.2 GeV/c. Likelihood method is used to discriminate the hadron shower and other events in the K L selection with the electromagnetic calorimeter. Using K L ʹs selected by these methods, we measured the B 0 → J / ψ + K L events, and obtained the CP-violation parameter, sin 2 φ 1 = 0.80 ± 0.13 ( stat ) .