Mass and width of the W Boson

The W Boson is a fundamental component of the Standard Model. The Standard Model makes predictions of the W Boson's properties. Measuring these properties ideally will give insights leading to a new era of physics.;The data used in this thesis was collected by the L3 detector at CERN's LEP collider during 1997. The center of mass energy for the colliding electron and positron was 183 GeV. The first part of this thesis describes a selection and a cross section measurement of W pair events decaying to the final state of a muon, a neutrino and two quarks. The second part presents a measurement of the W Boson mass and width from direct reconstruction using several W pair final states. The measured cross section, W mass and W width are se+e-→qqmn =2.31+/-.24pb MW=80.54+/-.16 GeV GW=2.06+/-.41 GeV .;These values are consistent with other experimental results from CERN and Fermila They are also consistent with Standard Model expectation based on lower energy data.