Measurement of the e+e- -> W+W- cross section and W decay branching fractions at LEP

Understand

From a total data sample of 701.1 pb^-1 recorded with e+e- centre-of-mass energies of sqrt = 161-209 GeV with the OPAL detector at LEP, 11693 W-pair candidate events are selected.

• These data are used to obtain measurements of the W-pair production cross sections at 10 different centre-of-mass energies.
• The ratio of the measured cross sections to the Standard Model expectation is found to be: data/SM = 1.002 +- 0.011(stat.) +- 0.007(syst.) +- 0.005(theory), where the uncertainties are statistical, experimental systematics and theory systematics respectively.
• The data are used to determine the W boson branching fractions, which are found to be consistent with lepton universality of the charged current interaction.