Ahn J. K. et al. (KOTO Collaboration)YEE HSIUNG2021-07-282021-07-282021319007https://www.scopus.com/inward/record.uri?eid=2-s2.0-85103521442&doi=10.1103%2fPhysRevLett.126.121801&partnerID=40&md5=bc2d85c3abda12888f7eba988a911370https://scholars.lib.ntu.edu.tw/handle/123456789/575022The rare decay KL 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±0.05stat±0.66syst)×10-10, three candidate events were observed in the signal region. After unveiling them, contaminations from K± and scattered KL 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 KL→ π0ν ν at the 90% confidence level. ? 2021 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.Atomic physics; Branching fractions; Confidence levels; Rare decays; Single event; Upper limits; Physics; article; contamination; expectationjournal article10.1103/PhysRevLett.126.121801338347962-s2.0-85103521442