Title:

Measurement of the leptonic angular distribution in Wboson decay as a function of the W transversemomentum using the CDF detector at the Tevatron

A measurement of the angular distribution of leptons from the analysis of Wboson decay data is presented. Although the properties of the leptonic angular distribution from W decays have been studied extensively in the past decades, the amount of data collected at the Tevatron is sufficient to observe Quantum Chromo Dynamics (QCD) corrections. When QCD is included, the lepton polarangle distribution is best described by two parameters, α1 and α2, functions of pWT: (dσ/d cosθ*) α (1 ± α1 cosθ* + α2 cos2θ*) where θ* is measured in the W restframe with respect to the proton beam. Both the W asymmetry measurement and the W mass precision measurement at CDF rely on the accurate understanding and simulation of the leptonic angular distribution. The data analysed in this thesis, which include both the electron and the muon channels, were collected with the CDF detector at the Tevatron protonantiproton collider during Run Ib (19941996). The coefficient α2 of the polarangle distribution is measured as a function of the Wboson transversemomentum up to 100 GeV. The measurement strategy consists of fitting the transversemass distribution to a set of templates from a Monte Carlo event and detector simulation. A loglikelihood method is used to determine α2. The measured values of α2 confirm the Standard Model expectation for the Wpolarisation at high transversemomentum. A study for a measurement of α1 is also presented. However, there is insufficient sensitivity for the measurement of α1 with the CDF Run I detector.
