I am working on the Simulated dataset ZZTo4eJJ (CERN Open Data Portal) to reconstruct the four-lepton invariant mass. When I extracted the electrons from ‘GSFelectrons’ and plotted the multiplicity distribution(n_l), I saw there were peaks corresponding to n_l < 4 . I thought that for an MC sample with a 4- final electron state, it’s guaranteed to find at least 2 electrons and 2 positrons. Can someone explain why this isn’t the case? Does ZZTo4EJJ only imply that there were 4 electrons at the generator level and not that HLT level algorithms detected four electronlike objects?
Hi! The simulated datasets include not only the process in question but also the underlying event (i.e. the interactions of the remaining partons of the proton that are not part of the hard process) and pile-up events (i.e. simultaneous collision). ZZTo4eJJ indicates the process that has been simulated, but then it (and what comes from the underlying event and from pile-up) is passed through the detector simulation and the outcome is in the same format as the for real collision events. The particle candidates (e.g. electrons) are then reconstructed from the signals left in different detectors. It may happen that the 4 electrons (in this case) do not pass the HLT selection.
Hope this helps!
Kati, for the CMS Open data team
Thank you so much for the clarification.