SMASH HepMC output is an implementation of the HepMC3 Event Record Library. The aim is to provide a format compatible with other frameworks like Rivet (https://rivet.hepforge.org). For resources regarding HepMC, see http://hepmc.web.cern.ch/hepmc/ and https://arxiv.org/abs/1912.08005.

Producing HepMC output requires HepMC3 to be installed. Download the tarball from http://hepmc.web.cern.ch/hepmc/ and follow the instructions.

ASCII HepMC Format

HepMC generally structures each event into particles and vertices connecting them, basically storing a graph of the event.

Two versions of HepMC are possible, if the HepMC format is specficified under Particles. The output only provides a particle list of the final state. For this only one central vertex is used. All initial state particles are incoming particles and all final state particles are outgoing particles of this vertex. Scatterings happening during the SMASH event are not recorded. For the collider modus, the intial state particles are combined into two single colliding nucleus "particles" with a nuclear pdg code.

In certain circumstances one may be interested in the full event structure. To that end, the output module provides the HepMC format also for the Collisions content. With this format, the full event tree is written. Furthermore, as above, for collider modus, we lump all incoming nucleons into nuclei, but split them out immediately afterwards to allow tracking of the individual nucleons.

In all cases, the module will track the number of binary, inelastic collisions between incident nucleons as well as keep track of participating incident nucleons.

You can find a snippet of the configuration for this output in Output Configuration.

The output is written in Asciiv3, the HepMC3 native plain text format. See https://arxiv.org/abs/1912.08005 for documentation of the format.

Note

Since some HepMC readers (e.g. Rivet) need a value for the nuclei-nuclei cross section, a dummy cross section of 1.0 is written to the output.
To avoid confusion with the definition of these quantities within the Glauber model, in the header of an event we set the numbers of participants and of collisions to -1.
If you use Fermi motion and want to read in the HepMC ouput into Rivet, you need to disable the check for the beam particle energies with the –ignore-beams option. When using the Rivet output this check is disabled by default.