pythia/decayer6/README.md

0001 \page Exampledecayer6 Example decayer6
0002
0003  This is an example of the external decayer implementation
0004  with PYTHIA6.
0005
0006  The complete PYTHIA6 documentation can be found at:
0007  https://pythia.org/
0008
0009  The PYTHIA6 external decayer was originally developed within
0010  the AliRoot framework, by Andreas Morsch (CERN).  \n
0011  The dependence on the ALICE software was taken off
0012  by Christian Holm Christensen.                    \n
0013  The dependence on the Root framework and the integration in
0014  the Geant4 framework was done by Ivana Hrivnacova (IPN Orsay).
0015
0016  <hr>
0017
0018  The use of the external decayer is demonstrated with using the
0019  classes from common examples repository, see below their complete
0020  list.
0021
0022  The G4Pythia6Decayer class provides the implementation of the
0023  G4VExternalDecayer interface with using PYTHIA6. In order
0024  to be able to use PYTHIA6, which is written in FORTRAN,
0025  a C++ interface class Pythia6 is provided. This class
0026  interfaces only the PYTHIA6 functions relevant to decay.
0027
0028  The G4Pythia6Decayer is instantiated in the
0029  P6DExtDecayerPhysics::ConstructProcess() function where the external
0030  decayer is set to G4Decay process for all particles.
0031  To demonstrate the decay with external decayer,
0032  the B- meson is defined in ExG4PrimaryGeneratorAction01,
0033  as it has no own decay table defined within Geant4.
0034
0035  With PYTHIA6, it is possible to force a selected decay
0036  type. This selection can be chosen interactively via
0037  the implemented Geant4 UI command:
0038 ```
0039 /pythia6Decayer/forceDecayType decayType
0040 ```
0041  where the available decay types  are listed in the EDecayType
0042  enumaration.
0043
0044  The classes Pythia6, G4Pythia6Decayer, G4Pythia6DecayerMessenger
0045  are independent from the example classes and can be reused
0046  in another user application.
0047
0048  Installation:
0049 - 1. Download the PYTHIA6 source file from the PYTHIA web site:\n
0050    https://pythia.org/
0051
0052    Note: The last tested version: 6.4.28
0053
0054 - 2A. With CMake: Build pythia6 library
0055
0056   For a convenience a CMake file for building Pythia6 library from
0057   the source is provided in
0058   examples/extended/eventgenerator/CMakeLists.txt.pythia6.
0059   Build the pythia6 library following the instructions in this file
0060   and then define the environment variables:
0061 ```
0062 PYTHIA6          the path where pythia6 library is installed
0063 PYTHIA6_VERSION  the pythia version
0064 ```
0065
0066 - 2B. With GNUmake: Define the environment variables: \n
0067 ```
0068 PYTHIA6           the path to pythia-versionX.f source code
0069 PYTHIA6_VERSION   the pythia version
0070 ```
0071
0072   e.g. If you download pythia-6.4.28.f.gz and unzip it in $HOME,
0073        then you have to set:
0074   ```
0075   export PYTHIA6=$HOME
0076   export PYTHIA6_VERSION="6.4.28"
0077   ```
0078   pythia6 will be then compiled together with example code.
0079
0080 - 3. Compilation:\n
0081   Then the example is compiled in a standard way, see
0082   [How to build and run an example](../../html/README_HowToRun.html).
0083   Note that with GNUmake build, an additional step 'gmake setup' is
0084   needed before 'gmake'.
0085
0086 - 4. Execution:
0087 ```
0088 % ./pythia6_decayer pythia6_decayer.in
0089 ```
0090
0091 This example uses the following user action classes from the extended examples 'common'
0092 repository:
0093  - Common::DetectorConstruction
0094  - Common::GunPrimaryGeneratorAction