What is the difference between GeneratedParticles and ReconstructedParticles?

[wdconinc]

Files created with the eicd and/or edm4hep data models contain both GeneratedParticles and ReconstructedParticles, and the GeneratedParticles are based on the ReconstructedParticle data type. What is the difference between them?

[wdconinc]

The edm4hep and derived eicd data models have one data type to store original 'truth' particle information, MCParticle (used by the MCParticles collection), and another data type to store the reconstructed particle information, ReconstructedParticle (used by the ReconstructedParticles collection).

Within edm4hep there is a way to connect collections of MCParticle and ReconstructedParticle data types using the MCRecoParticleAssociation association data type (used by e.g. the ReconstructedParticlesAssoc collection). A collection of these associations includes all identified links between the MCParticle and ReconstructedParticle collections.

Nevertheless, we considered it useful to add the original 'truth' particle information in the same structure as the reconstructed particle data type, so for all primary vertex particles in the MCParticles collection which are 'thrown' into the detector for simulation by geant4, we also create a collection of the ReconstructedParticle data type called GeneratedParticles. This collection GeneratedParticles typically contains fewer entries than the MCParticles collection because it does not contain internal or decayed particles of the primary event graph.