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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 cilinder placed inside the World volume. Follwoing 
UI commands are available to modify the geometry:

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

If geometry was changed between two runs, then the follwoing command need to
be executed:

/testhadr/update

By default beam direction coinsides 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 the PHYSLIST environment variable. By default 
QGSP_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 progectile 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

                          VISUALISATION

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 datebase, natural isotope 
composition is assumed. 

To use histograms any of implementations of AIDA interfaces should
be available (see http://aida.freehep.org).

For example, if iAIDA is installed and compiled at SLC4 Linux 

setenv AIDA_DIR  $MYPACKAGES/analysis/iAIDA/install/slc4_amd64_gcc34_root 
setenv PATH ${PATH}:${AIDA_DIR}/bin

Before compilation of the example it is optimal to clean up old 
object files:

gmake histclean
setenv G4ANALYSIS_USE 1
gmake

It is possible to choose the format of the output file with 
histograms using UI command:

/testhadr/HistoName   name
/testhadr/HistoType   type
/testhadr/HistoOption "uncompress"

The following types are available: hbook, root, aida. They will be 
stored in the file "name.hbook", "name.root", or "name.aida". 

To show the contence of a histogram ID=i the commands may be applied:

/testhadr/HistoPrint  i