Search for neutral and light new-particles through Kaon decays

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K05479
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Particle/Nuclear/Cosmic ray/Astro physics
• Research Institution: High Energy Accelerator Research Organization
• Principal Investigator: Komatsubara Takeshi 大学共同利用機関法人高エネルギー加速器研究機構, 素粒子原子核研究所, 教授 (30242168)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: K中間子 / 崩壊 / 稀崩壊 / 新粒子探索 / フレーバー物理 / ダーク

Outline of Final Research Achievements

We search for neutral and light new-particles X0 that appear through a two-body decay of long-lived neutral K meson, KL→π0X0, in the KOTO experiment at the Hadron Experimental Facility of Japan Proton Accelerator Research Complex, J-PARC. Based on the analysis of the data taken in 2015, new results on the KL→π0X0 decay were obtained and published. From the anaysis of the data taken in 2016-2018, we observed four candidate events in the signal region. Currently we are doing further checks on the four events and careful examinations on their origin.

Free Research Field

実験素粒子物理学

Academic Significance and Societal Importance of the Research Achievements

平成27年のデータをもとに得られたKL→π0X0崩壊の分岐比に対する上限値、X0の質量が135MeVの場合に90%の信頼水準で 4.2億回に一度、はこの崩壊に対する世界で最も低く厳しい値です。平成28-30年のデータで観測された四つの候補事象は、現在の分岐比の感度ではKL→π0νν崩壊ではなくKL→π0X0崩壊と解釈するのが自然です。いずれも、学術的意義が高く、自然法則の深い理解へさらに歩を進める結果です。