2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/37257From 1996 up to 2000 the LEP collider at CERN has operated at center of mass energies above the production threshold for W boson pairs of approximately 160 GeV. The obtained data are used to extract a preliminary W mass value of (80.450 +- 0.039) GeV by direct reconstruction. To a large extent the uncertainty is due to systematic effects especially in the fully hadronic decay channel W+W- --> qq' qq' that suffers most from ambiguities in modelling the hadronic final state. Methods to assess and reduce these uncertainties are the current main concern of the four LEP experiments.4 pages, 1 table (latex inc. moriond.sty), 3 figures (eps), to be published in the Proc. of the XXXVIIth Rencontres de Moriond "QCD and Hadronic interactions", Les Arcs, France, 2002High Energy Physics - Experimenttext