Muon-nuclear Interactions

Process and Cross Section

Muon-nuclear reactions in Geant4 are handled by the class G4MuonNuclearProcess. The default cross section class for this process is G4KokoulinMuonNuclearXS, the details of which are discussed in Muon Photonuclear Interaction.

Final State Generation

Just as for the electro-nuclear models, the final state generation for the muon-nuclear reactions proceeds in two steps. In the first step the electromagnetic vertex of the muon-nucleus reaction is calculated. Here the virtual photon spectrum is generated by sampling parameterized momentum transfer (\(Q^2\)) and energy transfer (\(\nu\)) distributions. In this case the same equations used to generate the process cross section are used to sample \(Q^2\) and \(\nu\). The equivalent photon method is then used to get a real photon.

In the second step, the real photon is interacted with the target nucleus at the hadronic vertex, assuming the photon can be treated as a hadron. Photons with energies below 10 GeV can be interacted directly with nucleons in the target nucleus using the measured \((\gamma, p)\) partial cross sections to decide the final state multiplicity and particle types. This is currently done by the Bertini-style cascade (G4CascadeInterface). Photons with energies above 10 GeV are converted to \(\pi^0\)s and then allowed to interact with nucleons using the FTFP model. In this model the hadrons are treated as QCD strings which collide with nucleons in the nucleus, forming more strings which later hadronize to produce secondaries. In this particular model the remnant nucleus is de-excited using the Geant4 precompound and de-excitation sub-models.

This two-step process is implemented in the G4MuonVDNuclearModel.