Possible reduction of the total uncertainty on the W boson mass measured at LEP2

An alternative W mass estimator in e+e- -> WW -> qqqq events at LEP2 is designed to optimize the balance between the statistical uncertainty and the systematic uncertainty due to a possible Colour Reconnection effect. The preliminary result for the total uncertainty on the W mass in this channel is roughly 30 % lower then those obtained with the standard estimators, based on the SKI implementation of Colour Reconnection. Also an indirect measurement of the SKI Colour Reconnection model parameter kappa is inferred from the difference between both W mass estimators.