Search for the $K_L\to {\pi }^0\nu \overline{\nu }$ Decay at the J-PARC KOTO Experiment

Journal Article · Tue Feb 25 19:00:00 EST 2025 · Physical Review Letters

DOI:https://doi.org/10.1103/PhysRevLett.134.081802· OSTI ID:2524072

Ahn, J. K.; Farrington, M.; Gonzalez, M.; Grethen, N.; Hanai, K.; Hara, N.; Haraguchi, H.; Hsiung, Y. B.; Inagaki, T.; Katayama, M.; Kato, T.; Kawata, Y.; Kim, E. J.; Kim, H. M.; Kitagawa, A.; Komatsubara, T. K.; Kotera, K.; Lee, S. K.; Li, X.; Lim, G. Y. ; Lin, C.; Luo, Y.; Mari, T.; Matsumura, T.; Morioka, I.; Nanjo, H.; Nishimiya, H.; Noichi, Y.; Nomura, T.; Ono, K.; Osugi, M.; Paschos, P.; Redeker, J.; Sato, T.; Sato, Y.; Shibata, T.; Shimizu, N.; Shinkawa, T.; Shiomi, K.; Shiraishi, R.; Suzuki, S.; Tajima, Y.; Taylor, N.; Tung, Y. C.; Wah, Y. W.; Watanabe, H.; Wu, T.; Yamanaka, T.; Yoshida, H. Y.

We performed a search for the $K_L\to {\pi }^0\nu \overline{\nu }$ decay using the data taken in 2021 at the J-PARC KOTO experiment. With newly installed counters and new analysis method, the expected background was suppressed to $0.252\pm {0.055}_{\mathrm{stat}}{}_{-{0.067}^{\mathrm{syst}}}^{+0.052}$ . With a single event sensitivity of $(9.33\pm 0.06_{\mathrm{stat}}\pm 0.84_{\mathrm{syst}})\times {10}^{-10}$ , no events were observed in the signal region. An upper limit on the branching fraction for the decay was set to be $2.2\times {10}^{-9}$ at the 90% confidence level (C.L.), which improved the previous upper limit from KOTO by a factor of 1.4. With the same data, a search for $K_L\to {\pi }^0{X}^0$ was also performed, where $X^0$ is an invisible boson with a mass ranging from 1 to $260\mathrm{MeV}/c^2$ . For $X^0$ with a mass of $135\mathrm{MeV}/c^2$ , an upper limit on the branching fraction of $K_L\to {\pi }^0{X}^0$ was set to be $1.6\times {10}^{-9}$ at the 90% C.L.

Published by the American Physical Society 2025

• Sponsoring Organization: USDOE
• Grant/Contract Number: SC0009798
• OSTI ID: 2524072
• Alternate ID(s): OSTI ID: 3011271
• Journal Information: Physical Review Letters, Journal Name: Physical Review Letters Journal Issue: 8 Vol. 134; ISSN 0031-9007; ISSN PRLTAO
• Publisher: American Physical Society
• Country of Publication: United States
• Language: English