Violates $\mathit CP$ in leading order. Test of direct $\mathit CP$ violation since the indirect $\mathit CP$-violating and $\mathit CP$-conserving contributions are expected to be suppressed. Test of $\Delta \mathit S$ = 1 weak neutral current.
1AHN 2025 result is based on data collected in 2021, which corresponds to $3.3 \times 10^{19}$ protons on target. A single event sensitivity of ($9.33$ $\pm0.06$ $\pm0.84$) $ \times 10^{-10}$ was achieved with no background events.
2AHN 2021 result is based on data collected in 2016, 2017 and 2018, which corresponds to $3.05 \times 10^{19}$ protons on target. A single event sensitivity of ($7.20$ $\pm0.05$ $\pm0.66$) $ \times 10^{-10}$ was achieved with 3 candidate events observed and total $1.22$ $\pm0.26$ background events.
3AHN 2019 result is based on data collected in 2015, which corresponds to $2.2 \times 10^{19}$ protons on target. A single event sensitivity of ($1.30$ $\pm0.01$ $\pm0.14$) $ \times 10^{-9}$ was achieved with no candidate events observed. An upper limit of $<$ $2.4 \times 10^{-9}$ at the 90$\%$ C.L. for the ${{\mathit K}_{{{L}}}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit X}^{0}}$ decay was also set, where ${{\mathit X}^{0}}$ is an invisible particle with a mass of 135 MeV/c${}^{2}$.
4AHN 2017 result is based on the first 100 hours of physics running in 2013. One candidate event was observed with an expected background of $0.34$ $\pm0.16$ events. An upper limit of $<3.7 \times 10^{-8}$ at the 90$\%$ C.L. for the ${{\mathit K}_{{{L}}}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit X}^{0}}$ decay was also set, where ${{\mathit X}^{0}}$ is an invisible particle with a mass of 135 MeV/c${}^{2}$.
5
Obtained combining Run-2 (AHN 2008) and Run-3 data.
6
Value obtained using data from February to April 2005.
7
Value obtained analyzing 10$\%$ of data of RUN 1 (performed in 2004).
References:
AHN
2025
PRL 134 081802
Search for the Decay at the J-PARC KOTO Experiment
AHN
2021
PRL 126 121801
Study of the $K_L \to \pi^0 \nu \bar \nu$ Decay at the J-PARC KOTO Experiment
AHN
2019
PRL 122 021802
Search for the $K_L \!\to\! \pi^0 \nu \overline{\nu}$ and $K_L \!\to\! \pi^0 X^0$ decays at the J-PARC KOTO experiment
AHN
2017
PTEP 2017 021C01
A New Search for the ${{\mathit K}_L^0}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \nu}}{{\overline{\mathit \nu}}}$ and ${{\mathit K}_L^0}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit X}^{0}}$ Decays
AHN
2010
PR D81 072004
Experimental Study of the Decay ${{\mathit K}_L^0}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \nu}}{{\overline{\mathit \nu}}}$
AHN
2008
PRL 100 201802
Search for the Decay ${{\mathit K}_L^0}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \nu}}{{\overline{\mathit \nu}}}$
AHN
2006
PR D74 051105
New Limit on the ${{\mathit K}_L^0}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \nu}}{{\overline{\mathit \nu}}}$ Decay Rate
Also
PR D74 079901 (errat.)
Publisher's Note to AHN 2006. New Limit on the ${{\mathit K}_L^0}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \nu}}{{\overline{\mathit \nu}}}$ Decay Rate
ALAVI-HARATI
2000
PR D61 072006
Search for the Decay ${{\mathit K}_L^0}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \nu}}{{\overline{\mathit \nu}}}$ using ${{\mathit \pi}^{0}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit \gamma}}$
