Speaker
Description
The KOTO experiment at J-PARC searches for the rare decay, $K_L → π^0ν\overlineν$. The mode is CP-violating, with a theoretical branching ratio highly suppressed in the Standard Model at $(2.94 ± 0.15) × 10^{−11}$. With a small theoretical uncertainty, this search is sensitive to new physics. In the analysis of 2016-2018 data, there were three observed events within the signal region, consistent with the background estimation. An upper limit on the branching ratio was set at < $4.8 × 10^{−9}$ (90% CL). Since that analysis, new hardware and analysis methods have been implemented to reduce the background level. The search in 2021 had a single event sensitivity of $8.66 × 10^{−10}$ which was comparable to 2016-2018 data taking. There were no events observed in the signal region, allowing KOTO to set the best upper limit on $BR(K_L → π^0ν\overlineν)$ to date at $< 1.99 × 10^{−9}$ (90% CL). I will report on the latest result of the $K_L → π^0ν\overlineν$ search from data taken in 2021.
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