Improved Standard-Model predictions for ${\eta }^{(\prime )}\to {\ell }^{+}{\ell }^{-}$

Noah Messerli, Martin Hoferichter, Bai-Long Hoid +2

The rare decays ${\eta }^{(\prime )}\to {\ell }^{+}{\ell }^{-}$, $\ell \in \{e,\mu \}$, are highly suppressed in the Standard Model, both by their chirality structure and the required loop attaching the…