Status on the Search for $K_L^0 \rightarrow \pi^0 \nu \bar{\nu}$ with the KOTO Experiment

Abstract

The KOTO experiment at the J-PARC research facility in Tokai, Japan aims to observe and measure the rare decay of the neutral kaon, $K_L^0 \rightarrow \pi^0 \nu \bar{\nu}$. This decay has a Standard Model (SM) predicted branching ratio (BR) of $(3.00 \pm 0.30) \times 10^{-11}$. While this decay is extremely rare, it is one of the best decays in the quark sector to probe for new physics beyond the SM due to small theoretical uncertainties. The E391a experiment at KEK 12-GeV PS previously searched for $K_L^0 \rightarrow \pi^0 \nu \bar{\nu}$ events and set a limit of BR($K_L^0 \rightarrow \pi^0 \nu \bar{\nu}$) $< 2.6 \times 10^{-8}$ in 2010. In 2018, KOTO set a new experimental limit of BR($K_L^0 \rightarrow \pi^0 \nu \bar{\nu}$) $< 3.0 \times 10^{-9}$ from data collected in 2015, improving the best experimental upper limit by an order of magnitude. From 2016 to 2018, KOTO collected around 1.5 times more data than in 2015, and the analysis of this dataset is underway. This report covers the progress and current status of the 2016-2018 data analysis.