$Id: README,v 1.1 2008/11/03 11:48:35 gcosmo Exp $
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 Example of the external decayer implementation with Pythia6
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 The complete Pythia6 documentation can be found at:
 http://home.thep.lu.se/~torbjorn/pythiaaux/recent.html
 
 The Pythia6 external decayer was originally developed within 
 the AliRoot framework, by Andreas Morsch (CERN).
 The dependence on the ALICE software was taken off
 by Christian Holm Christensen,
 The dependence on the Root framework and the integration in 
 the Geant4 framework was done by Ivana Hrivnacova (IPN Orsay).
 
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 The use of the external decayer is demonstrated on the modified
 novice N03 example.
 
 The G4Pythia6Decayer class provides the implementation of the
 G4VExternalDecayer interface with using Pythia6. In order
 to be able to use Pythia6, which is written in FORTRAN, 
 a C++ interface class Pythia6 is provided. This class
 interfaces only the Pythia6 functions relevant to decay.

 The G4Pythia6Decayer is instantiated in the ExN03PhysicsList class,
 in the ConstructDecay() function.
 To demonstrate the decay with external decayer,
 the B- meson is defined in ExN03PrimaryGeneratorAction,
 as it has no own decay table defined within Geant4.
 
 With Pythia6, it is possible to force a selected decay
 type. This selection can be chosen interactively via 
 the implemented Geant4 UI command:

 /pythia6Decayer/forceDecayType decayType

 where the available decay types  are listed in the EDecayType 
 enumaration.
 
 The classes Pythia6, G4Pythia6Decayer, G4Pythia6DecayerMessenger
 are independent from the example classes and can be reused 
 in another user application.
 
 Installation:
 
 1. Download the Pythia6 source file from the Pythia6 download site:
    http://www.hepforge.org/downloads/pythia6
    
 2. Define the environment variables:
    PYTHIA6           the path to pythia-vesrinX.f source code
    PYTHIA6_VERSION   the pythia version 
    
    e.g. If you download pythia-6.4.18.f.gz and unzip it in $HOME,
         then you have to set:
    export PYTHIA6=$HOME
    export PYTHIA6_VERSION="6.4.18"
    
 3. cd $G4INSTALL/example/extended/eventgenerator/pythia/decayer6
    make
 
 
 Execution:
 
 %  pythia6_decayer pythia6_decayer.in