학술논문
Search for $K_L \!\to\! \pi^0 \nu \overline{\nu}$ and $K_L \!\to\! \pi^0 X^0$ Decays at the J-PARC KOTO Experiment
Document Type
Working Paper
Author
KOTO Collaboration; Ahn, J. K.; Beckford, B.; Beechert, J.; Bryant, K.; Campbell, M.; Chen, S. H.; Comfort, J.; Dona, K.; Hara, N.; Haraguchi, H.; Hsiung, Y. B.; Hutcheson, M.; Inagaki, T.; Kamiji, I.; Kawasaki, N.; Kim, E. J.; Kim, J. L.; Kim, Y. J.; Ko, J. W.; Komatsubara, T. K.; Kotera, K.; Kurilin, A. S.; Lee, J. W.; Lim, G. Y.; Lin, C.; Lin, Q.; Luo, Y.; Ma, J.; Maeda, Y.; Mari, T.; Masuda, T.; Matsumura, T.; Mcfarland, D.; McNeal, N.; Micallef, J.; Miyazaki, K.; Murayama, R.; Naito, D.; Nakagiri, K.; Nanjo, H.; Nishimiya, H.; Nomura, T.; Ohsugi, M.; Okuno, H.; Sasaki, M.; Sasao, N.; Sato, K.; Sato, T.; Sato, Y.; Schamis, H.; Seki, S.; Shimizu, N.; Shimogawa, T.; Shinkawa, T.; Shinohara, S.; Shiomi, K.; Su, S.; Sugiyama, Y.; Suzuki, S.; Tajima, Y.; Taylor, M.; Tecchio, M.; Togawa, M.; Tung, Y. C.; Wah, Y. W.; Watanabe, H.; Woo, J. K.; Yamanaka, T.; Yoshida, H. Y.
Source
Phys. Rev. Lett. 122, 021802 (2019)
Subject
Language
Abstract
A search for the rare decay $K_L \!\to\! \pi^0 \nu \overline{\nu}$ was performed. With the data collected in 2015, corresponding to $2.2 \times 10^{19}$ protons on target, a single event sensitivity of $( 1.30 \pm 0.01_{\rm stat} \pm 0.14_{\rm syst} ) \times 10^{-9}$ was achieved and no candidate events were observed. We set an upper limit of $3.0 \times 10^{-9}$ for the branching fraction of $K_L \!\to\! \pi^0 \nu \overline{\nu}$ at the 90% confidence level (C.L.), which improved the previous limit by almost an order of magnitude. An upper limit for $K_L \!\to\! \pi^0 X^0$ was also set as $2.4 \times 10^{-9}$ at the 90% C.L., where $X^0$ is an invisible boson with a mass of $135~{\rm MeV}/c^2$.
Comment: 6 pages, 4 figures; published version, no change in the results. Fig. 1, Fig. 2, and Fig. 3 were revised, and Fig. 4 presenting the $K_L \!\to\! \pi^0 X^0$ limit as a function of the $X^0$ mass was added
Comment: 6 pages, 4 figures; published version, no change in the results. Fig. 1, Fig. 2, and Fig. 3 were revised, and Fig. 4 presenting the $K_L \!\to\! \pi^0 X^0$ limit as a function of the $X^0$ mass was added