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Supported file formats
ProMC file format
PROMC file format is used since 2014. It is primary used to to keep EVGEN records (truth level). The format uses Google protocol buffers. It uses varints for integers (and for 4-momenta and vertex). It's efficient format for events with large number of particles. The file sizes are typically 30% smaller than traditional ROOT with fixed bytes for floats and integer values.
ProIO file format
PROIO file format is used since 2018. It is more efficient file format then ProMC when the number of events in the files larger than 64k, and when number of particles in files is not large.
ROOT file format
ROOT files are used to keep fast detector simulations from Delphes
LCIO file format
LCIO files are used to keep simulated and reconstructed events for Geant4 simulation (and reconstruction) using “all-silicon” detector deigns.
LHE file format
LHE file formats are typically used for parton-level events from Madgraph.