The Muon Pair Production by other particles than muon is missing

[sudojan]

Currently, the parametrization of muon pair production is only valid for muons as the primary particle.
However, for the muon production in electromagnetic showers, it is also necessary to include parameterizations valid for electrons and positrons as well as photons as the primary particle. (Taus might be not so important for now.)

[Jean1995]

At least the muon pair production by photons will be included with #265

[asandrock]

The electron pair production by electrons is a very suppressed process, the contribution to dE/dX is about 1e-2 of the bremsstrahlung contribution; if we now take into account the suppression by the muon mass, we have on top of that a factor of (m_e/m_mu)^2 ~ 1e-4, i.e. a correction of relative magnitude about 1e-6. I therefore expect that direct production of muon pairs is strongly suppressed compared to emitting a bremsstrahlung photon and producing a muon pair via photoproduction.