Date of Award
5-2013
Document type
dissertation
Access Type
Open Access Dissertation
Degree Name
Doctor of Philosophy (PhD)
Degree Program
Physics
First Advisor
Benjamin Brau
Second Advisor
Stephane Willocq
Third Advisor
John Donoghue
Subject Categories
Physics
Abstract
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 = &sigmaWBR(W&rarr&mu&nu) / (&sigmaZBR(Z&rarr&mu&mu)) 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 Blackhat+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 Blackhat+Sherpa over-estimates the ratio Rjet by 12%.
DOI
https://doi.org/10.7275/hajk-3c15
Recommended Citation
Meade, Andrew Robert, "A Measurement of the W/Z Cross Section Ratio as a Function of Hadronic Activity with the ATLAS Detector" (2013). Open Access Dissertations. 757.
https://doi.org/10.7275/hajk-3c15
https://scholarworks.umass.edu/open_access_dissertations/757