Light-quark and Gluon Jet Discrimination in pp Collisions at $\sqrt{s} = 7$ TeV with the ATLAS Detector

ATLAS has developed a likelihood for the discrimination of quark-jets and gluon-jets using jet shape and tracking information. This poster describes the construction of the quark/gluon tagger and its validation using $4.7~fb^{−1}$ of proton-proton collision data at $\sqrt{s} = 7$ TeV collected with the ATLAS detector at the LHC. Data samples with enriched quark or gluon content are used in the construction and validation of templates of jet properties that are the input to the likelihood. The performance of the discriminator is established in both data and Monte Carlo simulation within a systematic uncertainty of ≈20%. A gluon-jet efficiency of ≈25% is attainable in data with an efficiency of ≈50% to select light-quark jets. The rejection of gluon-jets found in the data is far below what is attainable using some Monte Carlo simulations, where gluon-jet efficiencies of 10% can be reached for a 50%-efficiency selection of light-quark jets using the same jet properties.