[MAP] G4beamline Validation Document

[Tom Roberts]

A new document describing the many tests of G4beamline has been written, and is 
available at:
     http://www.muonsinc.com/g4beamline/G4beamlineValidation.pdf
The lack of such documentation was a major point from the MAP review, and this 
should resolve most of that concern.

Please send me any questions, comments, or suggestions you might have. In 
particular, what additional tests should be included in this document?

After a comment period (and possible re-work or additions), this will be 
contributed as a MuCool note. I intend to give a presentation on it at a future 
MAP Friday meeting. This will also be kept up-to-date and included in future 
G4beamline distributions.

In short:

   * The only major problem found is in the "cosmicraybeam" command.
     This does not affect any existing MAP simulations. Fixing it is
     on the ToDo list with low priority.

   * For multiple scattering, there are minor discrepancies between the
     MuScat data and the G4beamline/Geant4 results. The differences are in
     the sides, not the tails; it's not clear to me how important this is.

   * For energy loss of mu+ in copper, there is a factor of 2 discrepancy
     between the PDG model and the G4beamline/Geant4 results, for momenta
     above 100 GeV/c (below that they agree quite well). Fixing this is on
     the ToDo list with medium priority.

   * For proton straggling, there are modest discrepancies between data
     and the G4beamline/Geant4 results. It's not clear to me how
     important this is.

   * There are concerns about the accuracy and validity of the hadronic
     interaction models, especially for thick targets. The Geant4
     Collaboration continues to work on this.

Two new features have made it much easier to make sanity checks of magnets: a) a 
new command to draw field lines, and b) support for transparency in Open 
Inventor, making it possible to see daughter objects, field lines, and tracks 
inside objects (without the distracting lines from wireframe mode).


Tom Roberts