Prepared by R.Kokoulin, May 22nd, 2000

Brief summary of G4 muon activity, May 2nd - May 23rd, 2000
S.Kelner, R.Kokoulin, M.Maire, A.Rybin, L.Urban

1. G4 muon tests
The test procedure of the verification of muon interaction simulation which allows to check 
both mean free path calculation and energy transfer sampling has been suggested and 
implemented.
First test results revealed appreciable deviations of the distributions of the energy loss from 
theoretical dependencies (for bremsstrahlung, pair production, nuclear interaction). Several bugs 
have been found and eliminated; it has greatly improved the agreement.
The program of further G4 muon tests has been prepared and agreed, including thin target 
tests (extending the set of materials, energies, and increasing statistics), and thick target 
simulation which will allow to verify the consistency of consideration of restricted continuous 
energy loss.

2. Refinement of the processes already implemented
Simple formulae and algorithm for sampling photon and muon angles in muon 
bremsstrahlung have been suggested and prepared for implementation in G4. It will be coded in 
the nearest days.
Final states for other processes (pair production, photonuclear interaction) have been 
clarified, fixed and introduced into documentation.
Logical scheme of a consistent inclusion of bremsstrahlung correction in high-energy knock-
on electron production and ionisation energy loss is prepared.
List of questions concerning the validity of multiple scattering model has been compiled. 
After answering these questions, the "calibration" simulation of MCS for high-energy muons can 
be performed.

3. Documentation
Sections concerning three basic muon interaction processes (bremsstrahlung, pair production, 
photonuclear interaction) for PRM (Phys. Ref. Manual) have been extended, updated and 
corrected.
Suggestions for improvements for the section in PRM about muon ionisation, and also 
comments and corrections for "Electromagnetic Physics" gallery have been prepared.

4. Extension of the muon interactions in G4
List of muon processes for further inclusion in G4 has been discussed. The processes of 
interest are: muon pair production by photon, muon pair production by muon, diffractive 
bremsstrahlung (which leads to a difference in positive/negative muon energy loss). Refinement 
of multiple scattering and introduction of the  screening correction to bremsstrahlung and pair 
production based on recent calculations of radiation logarithm in HF model are also important 
and can improve the accuracy of G4-based simulations. The level of theoretical knowledge of 
these processes is sufficient for their implementation into algorithms and codes.
Theoretical clarification of LPM and Coulomb corrections for electron pair production by 
muons is needed; these are important both for accelerator and high-energy cosmic ray 
applications.