Measurement Of Diboson WZ Production Cross Section With The ATLAS Detector

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 Monte-Carlo simulated data of proton-proton collisions. The SM predicts the total W+Z production cross section to be 29.4 pb and the W?Z production cross section to be 18.4 pb. The 14 TeV center-of-mass energy proton-proton collisions are provided by the CERN (European Organization for Nuclear Research) LHC (Large Hadron Collider). The W and Z particles are detected using the ATLAS (A Toroidal LHC ApparatuS) detector. The studies use the ATLAS Computer System Commissioning (CSC) Monte Carlo datasets, which include trigger information and detector calibration and alignment corrections. The measurement uses the trilepton (eeνe, eeμν,μμeνandμμμν) 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 presented in detail. For the data of 1 fb?1 integrated luminosity, we expect to observe 53 W±Z signal events and 8 background events, giving a signal to background ratio of about 6.7. The WZ diboson production cross section for pp→WZ + X at S = 14 TeV is measured to beσ?Br =53. 43+?160.5.0fb(include event selection efficiency). This is in agreement with the predicted SM cross section. Meanwhile, a new data analysis technique, Boosted Decision Tree (BDT), is employed for WZ analysis, and it is also demonstrated that how to use TMVA (Toolkit for Multivariate Analysis) package to do data analysis.