True muonium resonant production at e ⁺ e ⁻ colliders with standard crossing angle

Abstract

True muonium (μ+μ-) is the heaviest and smallest bound state not containing hadrons, after true tauonium (τ+τ-) and mu-tauonium (μ+τ-).
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 (θ ~ 30°) 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 can be observed in relatively large quantities (O(10)/month) at a e+e- collider with standard crossing angle, after setting their center-of-mass energy to the TM mass (2mμ=211.4 MeV).