Scouring meson decays for true muonium

Rare meson decay experiments promise to measure branching ratios as small as $10^{-13}$. This presents an opportunity to discover the $μ^+μ^-$ bound state true muonium. We consider a set of possible channels, all with branching ratios above $\sim10^{-11}$. For the electromagnetic decays $η/η'\rightarrow(μ^+μ^-)γ$, theoretical and phenomenological form factors $F_{η/η'γγ^*}(Q^2)$ allow predictions of $\mathcal{BR}(η'\rightarrow (μ^+μ^-) γ)\sim 4.8\times10^{-10}$ and $\mathcal{BR}(η'\rightarrow (μ^+μ^-) γ)\sim 3.7\times10^{-11}$ at the 5% level. Discussion of experimental prospects and potential backgrounds are made.