PoS - Proceedings of Science
Volume 445 - 21st Conference on Flavor Physics and CP Violation (FPCP2023) - Kaon
KOTO: Search for Direct $CP$ Violating $K_L \to \pi^0 \nu \overline{\nu}$ Decays
Y.B. Hsiung*  on behalf of the KOTO Collaboration
Full text: pdf
Pre-published on: September 21, 2023
Published on: November 14, 2023
We review the current status of JPARC KOTO experiment to search for very rare $K_L$ decays to $\pi^0 \nu \overline{\nu}$ which is a FCNC and direct $CP$ violating decay mode. KOTO has collected $K_L$ decay data with $30$~GeV high intensity proton beam on target at JPARC since 2015 with an increasing beam power yearly over this period up to $64.5$~kW. The results from 2016-2018 dataset published in 2021 ($BR < 4.9 \times 10^{-9}$) revealed three candidate events in the signal region with $1.22 \pm 0.26$ estimated background events, which is dominated by the contamination of upstream charged kaon decays and was verified in a dedicated 2020 run after installing upstream charged beam veto. More physics data have been accumulated since then. The status of blind analysis and background reductions is presented in this report with future beam power projections at JPARC as well as KOTO-DAQ upgrades. Plans for KOTO-II upgrades beyond the Standard Model sensitivity ($3 \times 10^{-11}$) are also discussed.
DOI: https://doi.org/10.22323/1.445.0019
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