On Quasipositronia
  Quasipositronia are atoms of simple hydrogenlike structure. They are not included in periodic table of elements. Examples of such atoms are positronium, muonium, antimuonium, mu- and pi- mesoatoms, dimuonium and tauonium. Such atoms as positronium, dimuonium, tauonium, muonium and antimuonium are specially interesting from the point of view of investigations of fundamental properties of matter. Their description is rather simple and in many aspects similar to each other. In this paper energy levels and decay widths of different decay channels of dimuonium and tauonium has been given. Cross section of production of these atomic systems in electron positron annihilation has been calculated. To search these atoms, required experimental conditions for initial beams and detectors has been found. 
A.A. Malik and I.S. Satsunkevich