Barate, R (reprint author), CNRS, IN2P3, LAPP, F-74019 Annecy Le Vieux, France.
The e(+)e(-) --> W+W- cross section is measured in a data sample collected by ALEPH at a mean centre-of-mass energy of 172.09 GeV, corresponding to an integrated luminosity of 10.65 pb(-1). Cross sections are given for the three topologies, fully leptonic, semi-leptonic and hadronic of a W-pair decay. Under the assumption that no other decay modes are present, the W-pair cross section is measured to be 11.7 +/- 1.2(stat.) +/- 0.3(syst.) pb. The existence of the triple gauge boson vertex of the Standard Model is clearly preferred by the data. The decay branching ratio of the W boson into hadrons is measured to be B(W --> hadrons) = 67.7 +/- 3.1(stat.) +/- 0.7(syst.) %, allowing a determination of the CKM matrix element \V-cs\ = 0.98 +/- 0.14(stat.) +/- 0.03(syst.). (C) 1997 Elsevier Science B.V.