Search for the Neutral Long-Lived Kaon Rare Decay KL -> pi0 nu nu-bar

Abstract

The goal of the KOTO experiment is to search for the direct CP violating decay mode, KL → π0νν, and to probe for physics beyond the Standard Model of the elementary particle physics by measuring the branching ratio of this decay. The data was analyzed by a blind analysis technique and determined a single event sensitivity of (1.30 ± 0.01stat. ± 0.14sys.) × 10−9 with 0.42 ± 0.18 background events in the signal region. No candidate events in the signal region was observed, which allows an upper limit of 3.0 × 10−9 to be set at 90% confidence level. This is more than an order of magnitude improvement from the previous result in the 2013 analysis with single event sensitivity of (1.28 ± 0.04stat. ± 0.13sys.) × 10−8 and upper limit of 5.1 × 10−8 at 90% confidence level. The analysis of the 2015 data will be discussed in this thesis.