APS tip sheet: The new fate of the kaon


Preliminary reports of an extremely rare decay of a subatomic particle called the kaon could challenge the standard model of particle physics


Credit: Kitahara et al., Physical Review Letters (2020)

This past September, researchers at KOTO reported four incidents of rare decays from a type of subatomic particle called a kaon. However, the decays should be too rare to detect yet, according to the standard model of particle physics–a theory that describes how matter interacts through fundamental forces like electromagnetism. The decays’ presence also violates a well-known theoretical connection between charged and neutral kaon decays, so particle theorists will not accept the findings until this discrepancy is resolved. Recently, scientists Kitahara et al. have found a potential explanation as to why KOTO recognized those rare decays while larger experiments have missed them. They suggest that because KOTO is smaller than other detectors, it may not fully capture the subsequent decay of a new particle from a neutral kaon decay if the new particle flies a long distance before it decays. The presence of such rare decays of the kaon, if confirmed by further experiments, could force physicists to modify the standard model.


New physics implications of recent search for KL ? π 0νν¯ at KOTO

Teppei Kitahara, Takemichi Okui, Gilad Perez, Yotam Soreq, and Kohsaku Tobioka

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