New Physics Implications of Recent Search for K_{L}→π^{0}νν[over ¯] at KOTO.

Abstract

The KOTO experiment recently reported four candidate events in the signal region of K_{L}→π^{0}νν[over ¯] search, where the standard model only expects 0.10±0.02 events. If confirmed, this requires physics beyond the standard model to enhance the signal. We examine various new physics interpretations of the result including these: (1)heavy new physics boosting the standard model signal, (2)reinterpretation of "νν[over ¯]" as a new light long-lived particle, or (3)reinterpretation of the whole signal as the production of a new light long-lived particle at the fixed target. We study the above explanations in the context of a generalized new physics Grossman-Nir bound coming from the K^{+}→π^{+}νν[over ¯] decay, bounded by data from the E949 and the NA62 experiments.