Latest Result of the K_L→π⁰νν Search at the KOTO Experiment

Chieh Lin^1*

¹Physics, National Taiwan University, Taipei, Taiwan

* Presenter:Chieh Lin, email:jay@hep1.phys.ntu.edu.tw

The KOTO experiment is searching for the K_L→π⁰νν decay, which is sensitive to New Physics beyond the Standard Model due to the small theoretical uncertainty. The K_L→π⁰νν signal requires two photon hits in the calorimeter and the absence of hits in other detector components. The events inside the signal region is not accessible to dispel the prejudice against the candidate events. To date, the best upper limit of the BR(K_L→π⁰νν) is 3.0 x 10^-9 at 90% confidential level, given by KOTO based on the data collected in 2015.

KOTO further improved the sensitivity with the data collected from 2016 through 2018. With the low background level prediction, we unfolded the signal box in 2019, and some signal candidates were observed. Therefore, we have scrutinized the sources of those candidate events and investigated the possible background sources that we might have missed. In this presentation, we will report the updated result with the feedback from 2020 special run.

Keywords: CP violation, flavor physics, rare decay, kaon