This is a simple simulation example showing how to run event simulation using the Pythia8 event generator in heavy-ion mode and use an external custom trigger. The external trigger makes use of the DeepTrigger functionality to allow the user to access the internals of the event generator to define the trigger. In this example, information about the impact parameter of the currently-generated Pythia8 heavy-ion event is used. The trigger selection defines impact parameters to be accepted according to a min-max range that can be adjusted from the command line.

The definition and configuration of the external DeepTrigger is performed by the function trigger_impactb_pythia8(double bMin = 0., double bMax = 20.) defined in the macro trigger_impactb_pythia8.macro.

The macro file and function names are specified via --configKeyValues setting TriggerExternal.fileName and TriggerExternal.funcName, respectively.

WARNING

Using a trigger is not always the most efficient way to deal with event generation. It is always advisable to find a way to bias the event-geneator process to save CPU time. In this case, the selection of a specific impact-parameter range in Pythia8 can lead to a large time spent in the event generation rather than in the simulation.