A new search for the $K_{L} \to \pi^0 \nu \overline{\nu}$ and $K_{L} \to \pi^{0} X^{0}$ decays

Understand

We searched for the $CP$-violating rare decay of neutral kaon, $K_{L} \to \pi^0 \nu \overline{\nu}$, in data from the first 100 hours of physics running in 2013 of the J-PARC KOTO experiment.

• One candidate event was observed while $0.34\pm0.16$ background events were expected.
• We set an upper limit of $5.1\times10^{-8}$ for the branching fraction at the 90\% confidence level (C.L.).
• An upper limit of $3.7\times10^{-8}$ at the 90\% C.L.