Measurement of the $WZ$ production cross section in proton-proton collisions at $\sqrt{s} = 7$ TeV and limits on anomalous triple gauge couplings with the ATLAS detector

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.