Additional processes definition in CepGen

This repository provides a simple skeletton of an implementation of a C++ process example in CepGen.

As for other CepGen-derived projects, the build system is CMake, and its "standard recipe".

If you are not using a precompiled version of CepGen (i.e. your version of CepGen is built from sources), the CEPGEN_PATH environment variable should be set to the base source directory:

export CEPGEN_PATH=/path/to/cepgen/install

Note

On LXPLUS, CepGen is part of the LCG standard stack since 2023. The setting up of your own instance is therefore not necessary, as it can be retrieved automatically using e.g. one of the nightly builds for cc9/gcc11:

export CEPGEN_PATH=/cvmfs/sft.cern.ch/lcg/nightlies/dev4/Sat/MCGenerators/cepgen/1.2.5patch2/x86_64-el9-gcc11-opt/

Then, the usual CMake build recipe can be used:

mkdir build
cd build
cmake ..
make [-j]

The resulting object is a shared library containing all requirements to define a process in CepGen's runtime environment. By default, the library name is set to CepGenProcessExample, overridable through the -DPROCESS_NAME=MyProcessName addition to the cmake command above, or directly in the CMakeLists.txt file.

Once compiled and linked into a .so, or .dll shared library, it can be loaded into the CepGen runtime environment and added into the processes collection through the -a argument of CepGen's main executable, or using the cepgen::loadLibrary statement in custom user-defined executables.

Two examples of steering cards for the factorised process case described in the CepGen documentation website are given, both for collinear partons emission, or for $k_{\rm T}$-factorised fluxes.

In the earlier case, one may e.g. use:

$CEPGEN_PATH/bin/cepgen -a libCepGenFortranProcess.so -i cards/dummy_coll_cfg.py

Note

In case you have trouble running the cepgen executable (e.g. $CEPGEN_PATH/bin/cepgen) due to a failure to open shared object files, you may enforce the dynamic linking and python search paths to find your CEPGEN_PATH, e.g.:

export LD_LIBRARY_PATH=$CEPGEN_PATH/lib64:$LD_LIBRARY_PATH
export PYTHONPATH=$CEPGEN_PATH/python:$PYTHONPATH