Measurement of the mass and width of the W boson

TL;DR

This paper reports precise measurements of the W boson's mass and width using data from the OPAL experiment at LEP, testing the Standard Model's predictions through multiple analysis methods.

Contribution

It provides the first combined measurement of W boson mass and width from direct reconstruction and cross-section dependence, including limits on final-state interactions.

Findings

W boson mass mw = 80.415 GeV with combined errors

W boson width gw = 1.996 GeV with combined errors

Results are consistent with Standard Model predictions

Abstract

The mass and width of the W boson are measured using e+e- -> W+W- events from the data sample collected by the OPAL experiment at LEP at centre-of-mass energies between 170 GeV and 209 GeV. The mass (mw) and width (gw) are determined using direct reconstruction of the kinematics of W+W- -> qqbarlv and W+W- -> qqbarqqbar events. When combined with previous OPAL measurements using W+W- -> lvlv events and the dependence on mw of the WW production cross-section at threshold, the results are determined to be mw = 80.415 +- 0.042 +- 0.030 +- 0.009 GeV gw = 1.996 +- 0.096 +- 0.102 +- 0.003 GeV where the first error is statistical, the second systematic and the third due to uncertainties in the value of the LEP beam energy. By measuring mw with several different jet algorithms in the qqbarqqbar channel, a limit is also obtained on possible final-state interactions due to colour reconnection effects in W+W- -> qqbarqqbar events. The consistency of the results for the W mass and width with those inferred from other electroweak parameters provides an important test of the Standard Model of electroweak interactions