G. Abbiendi et al., Measurement of W boson polarisations and CP-violating triple gauge couplings from W+W- production at LEP, EUR PHY J C, 19(2), 2001, pp. 229-240
Measurements are presented of the polarisation of W+W- boson pairs produced
in e(+)e(-) collisions. and of CP-violating WWZ and WW gamma trilinear gau
ge couplings. The data were recorded by the OPAL experiment at LEP during 1
998. where a total integrated luminosity of 183 pb(-1) was obtained at a ce
ntre-of-mass energy of 189 GeV. The measurements are performed through a sp
in density matrix analysis of the W boson decay products. The fraction of W
bosons produced with longitudinal polarisation was found to be sigma (L)/s
igma (total) = (21.0 +/- 3.3 +/- 1.6)% where the first error is statistical
and the second systematic. The joint W boson pair production fractions wer
e found to be sigma (TT)/sigma (total) = (78.1 +/- 9.0 +/- 3.2)%, sigma (LL
)/sigma (total) = (20.1 +/- 7.2 +/- 1.8)% and sigma (LL)/sigma (total) = (1
.8 +/- 14.7 +/- 3.8)%. In the CP-violating trilinear gauge coupling sector
we find <(<kappa>)over tilde> = -0.02 (+0.10)(-0.07), g(4)(z) = -0.02(-0.33
)(+0.32) and <(<lambda>)over tilde>(z) = -0.18(-0.16)(+0.24), where errors
include both statistical and systematic uncertainties. In each case the cou
pling is determined with all other couplings set to their Standard model va
lues except those related to the measured coupling via SU(2)(L) x U(1)(Y) s
ymmetry. These results are consistent with Standard Model expectations.