True muonium resonant production at $e^{+}{e}^{-}$ colliders with standard crossing angle

True muonium (${\mu }^{+}{\mu }^{-}$) is the heaviest and smallest bound state not involving quantum chromodynamics, after true tauonium (${\tau }^{+}{\tau }^{-}$) and mu-tauonium (${\mu }^{\pm }{\tau }^{\mp }$). Unlike atoms containing $\tau$ particles, the muon lifetime is long enough to allow observation of true muonium ™ decays and transitions. One of the proposed methods to observe the spin 1 fundamental state of TM, which has the smallest lifetime among TM spin 1 states, was to build an $e^{+}{e}^{-}$ collider with a large crossing angle ($\theta \sim {30}^{\circ }$) in order to provide TM with a large boost and detect its decay vertex in $e^{+}{e}^{-}$. The following paper will instead show that TM excited states ($n\ge 2$) can be observed in relatively large quantities ($\mathcal{O}$(10)/month) at a feasible $e^{+}{e}^{-}$ collider with standard crossing angles, after setting their center-of-mass energy to the TM mass ($\sim 2m_{\mu }=211.4$ MeV).