This directory contains examples for using HepMC as an interface with various Monte Carlo event generators, such as PYTHIA. It also include an example for demonstrating MC truth handling with HepMC.

Requirements for external software packages

HepMC

Tested version : 2.06.09
http://lcgapp.cern.ch/project/simu/HepMC/

Note: examples were tested only on Linux with gcc.

PYTHIA

Tested version 6.4.26
URL: http://www.thep.lu.se/~torbjorn/Pythia.html

Examples HepMCEx01 and HepMCEx02

class HepMCG4Interface

This class is derived from G4VPrimaryGenerator, and is a base class for primary generation via HepMC object.

protected members:

virtual HepMC::GenEvent* GenerateHepMCEvent()
Implement this method in his/her own concrete class. An empty event will be created in default.
void HepMC2G4(const HepMC::GenEvent* hepmcevt, G4Event* g4event)
service method for conversion from HepMC::GenEvent to G4Event
virtual G4bool CheckVertexInsideWorld(const G4ThreeVector& pos) const
We have to take care for the position of primaries because primary vertices outside the world volume give rise to G4Exception. If the default implementation is not adequate, an alternative can be implemented in your own class.

public members:

virtual void GeneratePrimaryVertex(G4Event* anEvent)
The default behavior is that a single HepMC event generated by GenerateHepMCEvent() will be converted to G4Event through HepMC2G4().

class HepMCG4AsciiReader / HepMCG4AsciiReaderMessenger (derived from HepMCG4Interface)

This derived class is for reading primary information from an Ascii file generated by HepMC.

class HepMCG4PythiaInterface / HepMCG4AsciiReaderMessenger (derived from HepMCG4Interface)

This derived class is for directly calling PYTHIA functions. Users can set parameters, initialize, generate, and terminate by command line operation.

Macros in examples

hepmc_pygen.in
process PYTHIA events(H->4mu) generated at every event.
hepmc_ascii.in
read pregenerated events from HepMC Ascii file (data/example_MyPythia.dat).

Installation

1. Download and install HepMC from:
http://lcgapp.cern.ch/project/simu/HepMC/
and define the environment variable:
```
HEPMC_DIR         the path to HepMC installation.
```
2. Download the PYTHIA6 source file from the PYTHIA6 download site:
http://www.hepforge.org/downloads/pythia6
2A. With CMake: Build pythia6 library

For a convenience a CMake file for building Pythia6 library from the source is provided in examples/extended/eventgenerator/CMakeLists.txt.pythia6. Build the pythia6 library following the instructions in this file and then define the environment variables:
```
PYTHIA6          the path where pythia6 library is installed
PYTHIA6_VERSION  the pythia version 
```
2B. With GNUmake: Define the environment variables:
```
PYTHIA6           the path to pythia-versionX.f source code
PYTHIA6_VERSION   the pythia version 
```
e.g. If you download pythia-6.4.26.f.gz and unzip it in $HOME, then you have to set: export PYTHIA6=$HOME export PYTHIA6_VERSION="6.4.26"

pythia6 will be then compiled together with example code.
3. Compilation:
Then the examples are compiled in a standard way, see How to build and run an example.

Examples

See more details in Example HepMCEx01 and Example HepMCEx02.

Notes

We attached a sample HepMC Ascii data file, "data/example_MyPythia.dat", which contains 10 PYTHIA events created by "data/example_MyPythia.cxx".

Example MCTruth

Application MCTruth demonstrating handling of Monte-Carlo truth information through the HepMC package.