Study of the Decay at the J-PARC KOTO Experiment
J. K. Ahn (Department of Physics, Korea University, Seoul 02841, Republic of Korea); B. Beckford (Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA); M. Campbell (Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA); S. H. Chen (Department of Physics, National Taiwan University, Taipei, Taiwan 10617, Republic of China); J. Comfort (Department of Physics, Arizona State University, Tempe, Arizona 85287, USA); et al - Show all 70 authors
The rare decay was studied with the dataset taken at the J-PARC KOTO experiment in 2016, 2017, and 2018. With a single event sensitivity of , three candidate events were observed in the signal region. After unveiling them, contaminations from and scattered decays were studied, and the total number of background events was estimated to be . We conclude that the number of observed events is statistically consistent with the background expectation. For this dataset, we set an upper limit of on the branching fraction of at the 90% confidence level.