Electroweak Measurements in Electron-Positron Collisions at W-Boson-Pair Energies at LEP

TL;DR

This paper reports precise electroweak measurements from LEP electron-positron collisions at energies up to 209 GeV, testing the Standard Model and determining W boson properties and gauge couplings.

Contribution

It combines data from four experiments to measure cross-sections and fundamental W boson parameters, providing new constraints on electroweak theory at unprecedented energies.

Findings

Measured W boson mass as 80.376 GeV

Set upper limits on final-state interaction effects

Determined W decay branching fraction and gauge couplings

Abstract

Electroweak measurements performed with data taken at the electron-positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3 fb$^{-1}$ collected by the four LEP experiments ALEPH, DELPHI, L3 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV. Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron-positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose-Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, $M_W$ and $\Gamma_W$, the branching fraction of W decays to hadrons, $B(W\to\mathrm{had})$, and the trilinear gauge-boson self-couplings $g^Z_1$, $\kappa_\gamma$ and $\lambda_\gamma$ are determined to be: M_W = 80.376 \pm 0.033 ~GeV \Gamma_W = 2.195 \pm 0.083 ~GeV B(W\to\mathrm{had}) = 67.41 \pm 0.27 % g^Z_1 = 0.984 ^{+0.018}_{-0.020} \kappa_\gamma = 0.982 \pm 0.042 \lambda_\gamma = -0.022 \pm 0.019