Evidence For Wz Production And A Measurement Of The Wz Production Cross Section PDF Download

This dissertation describes a test of the Standard Model (SM) of particle physics by measuring the probability, or cross section, of simultaneously producing a W boson and a Z boson from proton-antiproton collisions. The SM predicts the cross section of WZ production to be 3.68 ± 0.25 pb. The SM and physics of WZ production are described in Chapter 2 of this dissertation. The 1.96 TeV center-of-mass energy proton-antiproton collisions are provided by the Fermi National Accelerator Laboratory (FNAL) Tevatron Collider. The W and Z particles are detected using the D0 detector, which is described in Chapter 3. The data were collected by the detector during 2002-2006 corresponding to 1 fb−1 of p{bar p} collisions. This data set is described in Chapter 6. The measurement uses the trilepton (e[nu]ee, [mu][nu]ee, e[nu][mu][mu], and [mu][nu][mu][mu]) decay channels, in which a W decays to a charged lepton plus a neutrino and a Z decays to a pair of charged leptons. The W and Z particle selection criteria, detection efficiency, and background determination are described in Chapter 7. We observe 13 candidate events in 1 fb−1 of p{bar p} collisions. In this data set we expect to see 4.5 ± 0.6 background events, and we expect to see 9.2 ± 1.0 signal events. The probability of 4.5 ± 0.6 background events to fluctuate to 13 or more events is 1.2 x 10−3 which is a 3.0 [sigma] deviation from the background estimate. A log likelihood method is used to determine the most likely cross section as determined by the measured signal efficiencies, the expected backgrounds, and the observed data. Presented in Chapter 8 is a measurement of the cross section for p{bar p} → WZ + X at √s = 1.96 TeV. The WZ diboson production cross section is measured to be [sigma]{sub WZ} = 2.7{sub -1.3}{sup +1.7} pb. This is in agreement with the predicted Standard Model cross section.