1.
Phys Rev Lett
; 126(12): 121801, 2021 Mar 26.
Article
in English
| MEDLINE
| ID: mdl-33834796
ABSTRACT
The rare decay K_{L}âπ^{0}νν[over ¯] was studied with the dataset taken at the J-PARC KOTO experiment in 2016, 2017, and 2018. With a single event sensitivity of (7.20±0.05_{stat}±0.66_{syst})×10^{-10}, three candidate events were observed in the signal region. After unveiling them, contaminations from K^{±} and scattered K_{L} decays were studied, and the total number of background events was estimated to be 1.22±0.26. We conclude that the number of observed events is statistically consistent with the background expectation. For this dataset, we set an upper limit of 4.9×10^{-9} on the branching fraction of K_{L}âπ^{0}νν[over ¯] at the 90% confidence level.