Study of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>K</mml:mi><mml:mi>L</mml:mi></mml:msub><mml:mo stretchy="false">→</mml:mo><mml:msup><mml:mi>π</mml:mi><mml:mn>0</mml:mn></mml:msup><mml:mi>ν</mml:mi><mml:mover accent="true"><mml:mi>ν</mml:mi><mml:mo stretchy="false">¯</mml:mo></mml:mover></mml:math> Decay at the J-PARC KOTO Experiment
J. K. Ahn, Brian Beckford, M. Campbell, S. H. Chen, J. Comfort, Kristin Dona, Michael Steven Farrington, Kouzou Hanai, Naoya Hara, Hiroki Haraguchi, Y. Hsiung, M. Hutcheson, T. Inagaki, M. Isoe, I. Kamiji, Takemi Kato, E. J. Kim, J. Kim, H. M. Kim, T. K. Komatsubara, K. Kotera, S. K. Lee, J. W. Lee, G. Y. Lim, Q. S. Lin, C. Lin, Y. Luo, T. Mari, Takahiko Masuda, Takeshi Matsumura, Duncan McFarland, N. McNeal, K. Miyazaki, R. Murayama, K. Nakagiri, H. Nanjo, Han Nishimiya, Y. Noichi, T. Nomura, T. Nunes, M. Ohsugi, H. Okuno, Joseph Redeker, J. Sanchez, M. Sasaki, N. Sasao, Takahiro Sato, K. Satô, Y. Sato, Nobuhiro Shimizu, T. Shimogawa, T. Shinkawa, Shuichi Shinohara, K. Shiomi, R. Shiraishi, S. Su, Yasuyuki Sugiyama, S. Suzuki, Y. Tajima, M. Taylor, M. Tecchio, M. Togawa, T. Toyoda, Yu-Chen Tung, Quynh Vuong, Y. W. Wah, H. Watanabe, Takeharu Yamanaka, H. Y. Yoshida, L. Zaidenberg
Abstract
The rare decay K_{L}→π^{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}→π^{0}νν[over ¯] at the 90% confidence level.