Measurement of the W boson mass and production and decay properties in collisions at GeV
The OPAL Collaboration, K. Ackerstaff 8 et al.
8 CERN, European Organisation for Particle Physics, CH-1211 Geneva 23, Switzerland
Received: 8 September 1997
This paper describes the measurement of the W boson mass, , and decay width, , from the direct reconstruction of the invariant mass of its decay products in W pair events collected at a mean centre-of-mass energy of =172.12GeV with the OPAL detector at LEP. Measurements of the W pair production cross-section, the W decay branching fractions and properties of the W decay final states are also described. A total of 120 candidate events has been selected for an integrated luminosity of 10.36pb-1. The production cross-section is measured to be pb, consistent with the Standard Model expectation. The and final states are used to obtain a direct measurement of GeV. Assuming the Standard Model relation between and , the W boson mass is measured to be GeV. The event properties of the fully-hadronic decays of events are compared to those of the semi-leptonic decays. At the current level of precision there is no evidence for effects of colour reconnection in the observables studied. Combining data recorded by OPAL at -172GeV, the W boson branching fraction to hadrons is determined to be %, consistent with the prediction of the Standard Model. The combined mass measurement from direct reconstruction and from the production cross-sections measured at and GeV is GeV.