Measurement of the W boson mass and $W^+W^-$ production and decay properties in $e^+e^-$ collisions at $\sqrt{s} = 172\,$GeV

The OPAL Collaboration:     K. Ackerstaff - et al.

doi:doi:10.1007/s100520050093

2023 Impact factor 4.2

Particles and Fields

Eur. Phys. J. C 1, 395-424

Measurement of the W boson mass and $\ensuremath{{\rm W}^+{\rm W}^-}$ production and decay properties in $\vec{{\rm e}^+ {\rm e}^-}$ collisions at $\vec{\large\sqrt{s}} = 172$ GeV

The OPAL Collaboration, K. Ackerstaff⁸ et al.

⁸ CERN, European Organisation for Particle Physics, CH-1211 Geneva 23, Switzerland

Received: 8 September 1997

Abstract
This paper describes the measurement of the W boson mass, $\ensuremath{M_{{\rm W}}}$ , and decay width, $\ensuremath{\Gamma_{{\rm W}}}$ , 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 $\ensuremath{\sqrt{s}}$ =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 $\ensuremath{{\rm W}^+{\rm W}^-}$ events has been selected for an integrated luminosity of 10.36pb^-1. The $\ensuremath{{\rm W}^+{\rm W}^-}$ production cross-section is measured to be $\ensuremath{\sigma_{{\rm WW}}}=12.3\pm1.3 {\rm (stat.)}\pm0.3{\rm (syst.)}$ pb, consistent with the Standard Model expectation. The $\ensuremath{\ensuremath{{\rm W}^+{\rm W}^-}\rightarrow\ensuremath{{\rm q\overline{q}}}\ensuremath{\ell\overline{\nu}_{\ell}}}$ and ${\rm W^+W^-}$ $\to$ ${\rm q \overline q q \overline q}$ final states are used to obtain a direct measurement of $\ensuremath{\Gamma_{{\rm W}}}=1.30^{+0.70}_{-0.55}{\rm (stat.)}\pm0.18{\rm (syst.)}$ GeV. Assuming the Standard Model relation between $\ensuremath{M_{{\rm W}}}$ and $\ensuremath{\Gamma_{{\rm W}}}$ , the W boson mass is measured to be $\ensuremath{M_{{\rm W}}}=80.32\pm0.30{\rm (stat.)}\pm0.09{\rm (syst.)}$ GeV. The event properties of the fully-hadronic decays of $\ensuremath{{\rm W}^+{\rm W}^-}$ 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 $\ensuremath{\sqrt{s}}\sim161$ -172GeV, the W boson branching fraction to hadrons is determined to be $69.8^{+3.0}_{-3.2}{\rm (stat.)}\pm0.7{\rm (syst.)}$ %, consistent with the prediction of the Standard Model. The combined mass measurement from direct reconstruction and from the $\ensuremath{{\rm W}^+{\rm W}^-}$ production cross-sections measured at $\ensuremath{\sqrt{s}}\sim161$ and $\ensuremath{\sqrt{s}}\sim172$ GeV is $\ensuremath{M_{{\rm W}}}= 80.35 \pm 0.24{\rm (stat.)}\pm0.07{\rm (syst.)}$ GeV.