Search for a feebly interacting particle $X$ in the decay $K^{+}\to {\pi }^{+}X$

NA62 Collaboration

A search for the $K^{+}\to {\pi }^{+}X$ decay, where $X$ is a long-lived feebly interacting particle, is performed through an interpretation of the $K^{+}\to {\pi }^{+}\nu \bar{\nu }$…