geant4

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     Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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                                 HADR00

                             V.Ivanchenko
                       CERN, Geneva, Switzerland


This example demonstrates a usage of G4PhysListFactory to build 
Physics List and G4HadronicProcessStore to access cross sections.

                           GEOMETRY

The Target volume is a cylinder placed inside the World volume. Following 
UI commands are available to modify the geometry:

/testhadr/TargetMat     G4_Pb
/testhadr/WorldMat      G4_AIR
/testhadr/TargetRadius  10 mm
/testhadr/TargetLength  20 cm

By default beam direction coincides with the target axis and is Z axis 
in the global coordinate system. The beam starts in the middle of the target.
G4ParticleGun is used as a primary generator. The energy and the type of 
the beam can be defined via standard UI commands

/gun/energy   15 GeV
/gun/particle proton

                           PHYSICS

Physics List is defined by its name given in the 3d argument of the of the 
run command. 

Hadr00 my.macro QGSP_BERT   

If 3d argument is not set then by the PHYSLIST environment variable. 
By default FTFP_BERT Physics List will be instantiated.

 
                        CROSS SECTION

At the end of any run the set of cross sections is built and can be printed 
out for a given projectile particle and a target element, which can be 
defined via UI commands:

/testhadr/particle   pi+
/testhadr/targetElm  Pb
/testhadr/verbose    1

The level verbosity above zero provides printout of the cross section table.
The energy/momentum limits and number of bins can be set via UI commands:

/testhadr/nBinsE      900
/testhadr/nBinsP      700
/testhadr/minEnergy   1 keV
/testhadr/maxEnergy   1 TeV
/testhadr/minMomentum 1 MeV
/testhadr/maxMOmentum 10 TeV

                          VISUALIZATION

For interactive mode G4 visualization options and variables should be
defined, then the example should be recompiled:

gmake visclean
gmake

The vis.mac file can be used an example of visualization. The following 
command can be used:

/testhadr/DrawTracks  charged
/testhadr/DrawTracks  neutral
/testhadr/DrawTracks  all

                          HISTOGRAMS

All histograms are provided in decimal logarithmic scale (log10(E/MeV)
and log10(p/GeV)) for one projectile particle and one target element.
The element is taken from the Geant4 NIST database, natural isotope 
composition is assumed. 

It is possible to change scale and output file name using UI commands:

/testhadr/histo/fileName name
/testhadr/histo/setHisto idx nbins vmin vmax unit

Only ROOT histograms are available.