Search of K_L⁰→π⁰νν and K_L⁰→π⁰Χ⁰ Decays at the J-PARC KOTO Experiment

Chieh Lin^1*

¹Physics, National Taiwan University, Taipei, Taiwan

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

The KOTO experiment aims to search the rare kaon decay K_L⁰→π⁰νν , which is a CP-violating process and one of the best probes to search for new physics beyond Standard Model due to the small theoretical uncertainty. A single event sensitivity (S.E.S.) of (1.30 ± 0.01_stat. ± 0.14_syst.) × 10^-9 was achieved based on the data collected in 2015. No candidate event is observed with the expected background level (0.42 ± 0.18) and thus an upper limit of 3.0 × 10^-9 for the branching ratio of K_L⁰→π⁰νν at 90% confidence level (C.L.) is set [1]. The KOTO experiment is also sensitive to K_L⁰→π⁰Χ⁰, where X⁰ is an invisible light boson. An upper limit of 2.4 × 10^-9 at 90% C.L. is set for the X⁰ mass of 135 MeV/c². After 2015, a new photon veto detector was further implemented to reduce more kaon backgrounds. Also, the trigger that counts the number of electromagnetic showers in the CsI calorimeter was introduced to collect the data more efficiently. The number of collected kaons from 2016 to 2018 is about 1.5 times larger than that in 2015. The S.E.S. of 5 × 10^-10 for K_L⁰→π⁰νν is expected.

References
[1] The KOTO Collaboration et al. “Search of K_L⁰→π⁰νν and K_L⁰→π⁰Χ⁰ Decays at the J-PARC KOTO Experiment”. In: ArXiv e-prints (Oct. 2018). arXiv: 1810.09655 [hep-ex].

Keywords: Kaon, Flavor Physics, CP violation, Rare Decay