Speaker
Description
The KOTO experiment at the J-PARC is dedicated to searching for the rare decay $K_L\rightarrow \pi^0\nu\bar{\nu}$.
In the analysis of the data taken in 2021, no signal candidates were observed, and the world-best limit of $2.2×10^{-9}$ on the branching ratio was set at the 90% confidence level.
After the data taking in 2021, we improved our detectors to further suppress the charged kaon background, which was one of the main backgrounds in the analysis of the data taken in 2016-2018. The charged particle detector was upgraded to make it more sensitive to charged kaons in the beam. In addition, the permanent magnet was installed in the beam line to reduce the flux of charged kaons.
The DAQ system was also upgraded to improve its rate capability. A new trigger was implemented to take more control samples for the precise evaluation of the photon inefficiency in veto detectors, which is crucial to evaluate the number of $K_L \rightarrow 2\pi^0$ backgrounds. After these upgrades, we have accumulated the physics data during 2024-2025.
In this presentation, we will report the current status of the analysis of the 2024-2025 data, which has approximately twice the statistics of the previous analysis.