Speaker
Description
Rare decays of $K,B$ mesons provide a powerful probe of dark sectors with light new particles. We show that the pair production of $O(100\,{\rm MeV})$ dark states can be probed with the decays of $K_L$ mesons, owing to the enhanced two-body kinematics, $K_L\to X_1X_2$. If either or these two particles is unstable, {\em e.g.} $X_2\to X_1\pi^0$ or $X_{1,2}\to \gamma\gamma$, such decays could easily mimic $K_L\to \pi^0 \nu\overline{\nu}$ signatures, while not being ruled out by the decays of charged kaons. We construct explicit models that could account for the KOTO excess events, and pass all other constraints from collider searches and meson decays. The lightest of $X_{1,2}$ particles, in some models, could constitute the entirety of dark matter.
