Measurement of triple gauge WWgamma couplings at LEP2 using photonic events

A study of events with photons and missing energy has been performed with the data sample obtained with the ALEPH detector at centre-of-mass energies from 161 to 184 GeV,corresponding to a total integrated luminosity of about 80 pb**-1. The measured distributions are in agreement with Standard Model predictions, leading to constraints on W W gamma gauge coupling parameters Delta(kappa_gamma) and lambda_gamma. The results from the fit to the cross sections and to the energy and angular distributions of the photons are: Delta(kappa_gamma) = 0.05 +1.15/-1.10 (stat) +/- 0.25 (syst) lambda_gamma = 0.05 +1.55/-1.45 (stat) +/- 0.30 (syst)