Measurement of W-pair production in e+e- collisions at 189GeV

TL;DR

This paper reports on the measurement of W-pair production cross sections and decay branching fractions in electron-positron collisions at 189 GeV, providing tests of the Standard Model and CKM matrix elements.

Contribution

It provides the first precise measurement of W-pair production cross sections and W decay branching fractions at 189 GeV, including the determination of |V(cs)|.

Findings

Total W-pair cross section measured as 15.71 pb

W decay branching fraction into hadrons is 66.97%

CKM matrix element |V(cs)| is 0.951

Abstract

The production of W-pairs is analysed in a data sample collected by ALEPH at a mean centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 174.2 pb^-1. Cross sections are given for different topologies of W decays into leptons or hadrons. Combining all final states and assuming Standard Model branching fractions, the total W-pair cross section is measured to be 15.71 +- 0.34 (stat) +- 0.18 (syst) pb. Using also the W-pair data samples collected by ALEPH at lower centre-of-mass energies, the decay branching fraction of the W boson into hadrons is measured to be BR (W > hadrons) = 66.97 +- 0.65 (stat) +- 0.32 (syst) %, allowing a determination of the CKM matrix element |V(cs)|= 0.951 +- 0.030 (stat) +- 0.015 (syst).