IPNS and J-PARC Joint Invited Seminar : Latest results on the KL->pi0nunubar search at the J-PARC KOTO experiment

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Overview

The KOTO experiment at the J-PARC 30GeV Main Ring is dedicated to search for the rare decay KL->pi0nunubar.
This mode directly breaks the CP symmetry and is highly suppressed in the Standard Model (SM).
In addition, the theoretical uncertainty of this decay is only a few percent.
These features make this decay one of the best probes to search for new physics beyond the SM.

In the previous analysis on data taken in 2016-18, we observed three signal candidate events,
which was statistically consistent with the background expectation.
The largest background source was the charged kaon contamination in the neutral beam.
Because of that, we have installed a new counter to detect charged kaons since 2020.
We have also developed several new analysis methods to reduce other background events and estimated the contribution
of background events more precisely. In this presentation, we will focus on the analysis of data taken in 2021 whose statistics
correspond to a similar sensitivity of the previous analysis and report new results on the KL->pi0nunubar search.