Measurement of the triple gauge-boson couplings γWW and ZWW in ALEPH and at LEP

This document deals with the couplings between the W boson and Z and gamma particles. WWZ and WWγ vertex are predicted by the electroweak theory based on the symmetry group SU(2)L*U(1)Y, their existence is confirmed by the measurement of the production cross-section of W pairs at LEP. The effective values of the couplings are modified by the introduction of standard model particle loops at the vertex level, the impact on the coupling value is assessed to reach 10-3. These loops can also include beyond-the-standard-model particles, their impact is in the magnitude order of 10-3 for most models. The fully description of these loops requires the values of 14 complex parameters whose measurement will give information about the existence of new particles. Nevertheless the number of events at LEP is not sufficient to measure all the parameters simultaneously. As a consequence the analysis is limited to the 3 most promising parameters: g1Z, κγ and λγ. At LEP the events sensitive to these couplings are the final states WW and Weν. Their differential and total production cross-sections are the variables used to compute the value of couplings. The uncertainties on these measurements mainly stem from the angular distribution analysis of the final state WW → νqq. All the data collected by the ALEPH experiment has been processed. The combination of the measurement of the 4 LEP experiments (ALEPH, DELPHI, L3 and OPAL) leads to an uncertainty cut by half: g1Z = 0.991 (+0.022-0.021); κγ 0.984 (+0.042-0.047) and λγ = -0.016 (+0.021-0.023). (A.C.)