Measurement of triple gauge-boson couplings at LEP energies up to 189 GeV

The triple gauge-boson couplings involving the W are determined using data samples collected with the ALEPH detector at mean centre-of-mass energies of 183 GeV and 189 GeV, corresponding to integrated luminosities of 57 pb(-1) and 174 pb(-1), respectively. The couplings, g(1)(Z), kappa (gamma) and lambda (gamma) are measured using W-pair events, single-W production and single-gamma production. Each coupling is measured individually with the other two couplings fixed at their standard model value. Including ALEPH results from lower energies, the 95% confidence level intervals for the deviation to the standard model are -0.087 < Deltag(1)(Z) < 0.141, -0.200 < Delta kappa (gamma) < 0.258, and - 0.062 < lambda (gamma) < 0.147. Fits are also presented where two or all three couplings are allowed to vary. In addition, W-pair events are used to set limits on the C- or P-violating couplings g(4)(V), g(5)(V), <(<kappa>)over tilde>(V) and <(<lambda>)over tilde>(V), where Vdenotes either gamma or Z. No deviations from the standard model expectations are observed.