EPJ

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EPJ C - Particles and Fields
Particles and Fields


Eur. Phys. J. C 19, 229-240
DOI: 10.1007/s100520100602

Measurement of W boson polarisations and CP-violating triple gauge couplings from W+W- production at LEP

The OPAL Collaboration G. Abbiendi and et al.

Dipartimento di Fisica dell' Università di Bologna and INFN, 40126 Bologna, Italy

(Received: 18 August 2000 / Published online: 15 March 2001 -© Springer-Verlag 2001)

Abstract
Measurements are presented of the polarisation of ${\rm W}^{+}{\rm W}^{-}$ boson pairs produced in ${\rm e}^{+}{\rm e}^{-}$ collisions, and of CP-violating ${\rm WWZ}$ and ${\rm WW}\gamma$ trilinear gauge couplings. The data were recorded by the OPAL experiment at LEP during 1998, where a total integrated luminosity of 183 pb-1 was obtained at a centre-of-mass energy of 189 GeV. The measurements are performed through a spin density matrix analysis of the ${\rm W}$ boson decay products. The fraction of ${\rm W}$ bosons produced with longitudinal polarisation was found to be $\sigma_{\rm L}/\sigma_{\rm total} = (21.0 \pm 3.3 \pm 1.6)\%$ where the first error is statistical and the second systematic. The joint ${\rm W}$ boson pair production fractions were found to be $\sigma_{\rm TT}/\sigma_{\rm total} = (78.1 \pm 9.0 \pm 3.2)\%$, $\sigma_{\rm LL}/\sigma_{\rm total} = (20.1 \pm 7.2 \pm 1.8)\%$ and $\sigma_{\rm TL}/\sigma_{\rm total} = (1.8 \pm 14.7 \pm 3.8)\%$. In the CP-violating trilinear gauge coupling sector we find $\tilde{\kappa}_{\rm z} = -0.20^{+0.10}_{-0.07}$, $g^{\rm z}_{4} = -0.02^{+0.32}_{-0.33}$ and $\tilde{\lambda}_{\rm z} = -0.18^{+0.24}_{-0.16}$, where errors include both statistical and systematic uncertainties. In each case the coupling is determined with all other couplings set to their Standard Model values except those related to the measured coupling via $SU(2)_{\rm L}\times U(1)_{\rm Y}$ symmetry. These results are consistent with Standard Model expectations.



© Società Italiana di Fisica, Springer-Verlag 2001

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