How do I read the .hep file from Pythia?

The pythia_event.hep file is a file in the STDHEP format. Most of the time you don't need to read it - PGS and Delphes both understand STDHEP input by default, so you can just use it in these detector simulations. If you want to read it yourself, you can either use the ExRootAnalysis package to convert the file into a ROOT file, or edit the program pythia-pgs/src/hep2lhe.f. hep2lhe is an example program showing how to read the STDHEP file, convert it to Pythia format, perform jet clustering and other operations, and output the information as an LHE file. Please note that the LHE file that results from this program does NOT include all the information from the STDHEP file, and can not be used as input to a detector simulation.

-- Main.JohanAlwall - 2011-06-30

MadAnalysis5 is now interfaced to MG5aMC in v2.5.0 and can read stdhep files from Pythia6.