Pileup measurement and mitigation techniques in CMS

When trying to reconstruct an event from a hard-scatter pp collision in CMS, it is of the utmost importance to correctly measure the energy from jets. The jet energy corrections (JEC) correct, on average, the energy of the reconstructed jets back to the energy of the final-state particles that initiated the jets. This effort is hindered by additional energy in the jets coming from other soft pp collisions. The additional energy is termed pileup or offset and comes from everything except the primary vertex (PV) and its underlying event (UE). In this paper, we describe how this pileup energy is measured and parametrized as well as the techniques used to remove this extra energy from the reconstructed jets.