On the effects at colliding mu-meson beams
  Possible influence of the weak interaction on the $\mu^+ + \mu^- \to \mu^+ + \mu^- $ scattering and the $\mu^+ + \mu^- \to e^+ + e^- $ reaction, both through the neutral lepton currents and the charged ones (in the second order on weak constant), are considered.   The calculations show that $P$ - odd effects in the mentioned processes would prove the existence of the neutral currents which, in their turn, give the principal basis for explanation of the mass difference of a muon and an electron from the point of view of Ref. [1]. 
F.F. Tikhonin