Quark and Gluon Jet Separation and QCD Studies at CMS

Jets are among the most studied structures at hadron colliders. Their importance is due to the fact that they are involved in a large number of processes, and that they retain some memory of the properties of the parton they originate from. The ability to separate quark jets from gluon jets is an important tool for signal discrimination in analyses containing jets in their final state, like some typical decays of the Higgs boson. This separation, however, is not completely achievable due to the statistical nature of hadronization. Using variables obtained from the CMS Particle Flow algorithm, which allow an accurate reconstruction of jets with a high granularity, we can exploit the structural differences between quark and gluon hadronization to derive a likelihood-based discriminant which statistically separates quark from gluon jets. The performance of the discriminator is tested both on real and simulated data; some typical problems arising from high luminosity of the LHC (pileup) are also taken into account and corrected for.