Measurement of the WZ Production Cross Section in Proton-Proton Collision at \(\sqrt s = 7 TeV\) and Limits on Anomalous Triple Gauge Couplings with the ATLAS Detector

Abstract

In this dissertation, we present a study of WZ production in proton-proton collisions at a center-of-mass energy of 7 TeV. The data analyzed was collected by the ATLAS detector and corresponds to an integrated luminosity of \(4.6 fb^{−1}\) provided by the Large Hadron Collider in 2011. We select WZ events in the fully leptonic decay mode with electrons, muons, and missing transverse energy in the final state. Events are required to have three isolated leptons with significant transverse momentum, a large missing transverse energy, a Z candidate reconstructed from two of the selected leptons, and a W candidate reconstructed from the missing transverse energy and third lepton. The major backgrounds to the WZ signal in the leptonic decay channel are Z+jets events, ZZ production, Z+photon events, and events with top quarks. We estimate the Z+jets and top quark background contributions from data and take the expected contribution for the other background processes from simulation. We observe 317 WZ candidates in data, with a background expectation of \(68\pm10\) events. The total production cross section is extracted from the selected sample using a maximum likelihood method and is determined to be \(19.0^{+1.4}_{-1.3} (stat) \pm0.9 (syst) \pm0.4 (lumi) pb\), which is consistent with the next-to-leading Standard Model prediction of \(17.6^{+1.1}_{-1.0} pb\). WZ production in the Standard Model includes a contribution from the WWZ triple gauge boson vertex. If new physics beyond the Standard Model exists and interacts with W and Z bosons, the coupling of the WWZ vertex could differ from the Standard Model prediction. We set limits on anomalous triple gauge boson couplings using the transverse momentum spectrum of Z bosons in the selected sample. We derive the 95% confidence interval for three model-independent anomalous triple gauge couplings using a frequentist approach and set the most stringent bounds to date on two of the three parameters.