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A measurement of the W/Z cross section ratio as a function of hadronic activity with the ATLAS detector
Hadronic collisions at the LHC at CERN probe particle interactions at the highest energy scale of any experiment to date. We present a research program measuring Rjet = [special characters omitted] as a function of a number of hadronic variables. The measurements are performed with the ATLAS detector at the LHC, using the 2011 data set, consisting of 4.64 fb-1 of pp collisions at a center of mass energy of 7 TeV. This measurement is a robust way to test the Standard Model and the modeling of perturbative QCD, and is sensitive to a wide variety of possible new physics in events with high jet ET, including some variations of Supersymmetry. By taking the ratio of W/Z production, a large number of systematic uncertainties cancel, including those associated with luminosity, jet energy scale and resolution, and many theoretical uncertainties. The measurement of Rjet is performed as a function of the pT and rapidity of the 1st-4th leading jet, ST, HT, and a number of dijet variables, including invariant mass and angular separations. The measurements are compared with NLO theoretical predictions from BLACKH AT+SHERPA, as well as using leading order simulations from ALPGEN and SHERPA. Over most of the kinematic phase-space, there is good agreement between the data and theoretical predictions. There is a significant deviation for exactly one selected jet above 30 GeV, where LACKHAT+SHERPA over-estimates the ratio Rjet by 12%.
Meade, Andrew, "A measurement of the W/Z cross section ratio as a function of hadronic activity with the ATLAS detector" (2013). Doctoral Dissertations Available from Proquest. AAI3589096.