KOTO Experiment at J-PARC Hadron Experimental Facility Broke World’s Best Sensitivity on Rare Neutral Kaon Decay by an Order of Magnitude

First step forward elucidation of “matter-antimatter asymmetry”

Notable Points

• In the J-PARC experiment, the collaboration achieved the improvement by an order of magnitude in the sensitivity to search for the rare neutral-kaon decay.
• The collaboration has begun to elucidate the matter-antimatter asymmetry (CP symmetry breaking) in the universe through kaon decays

Synopsis

An international collaboration reported the first major results from the experiment KOTO, which is being conducted at the Hadron Experimental Facility of Japan Proton Accelerator Research Complex (J-PARC). The KOTO collaboration set the upper limit of once in three hundred million on the rate of the neutral K-meson (kaon) decay into a neutral pi meson and a pair of neutrinos from the analysis of the data set collected in 2015, and improved the world’s best sensitivity by an order of magnitude. The collaboration has begun to elucidate the matter-antimatter asymmetry (CP symmetry breaking) in the universe through kaon decays. As the prospects for future, further improvements on the sensitivity with data collected since 2016 are anticipated. The collaboration upgraded the KOTO detector in the autumn of 2018, and started to take the new data with it in February 2019.

The results have been published in the 18-January-2019 issue of the journal Physical Review Letters.

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