Influence of 5-jet events on the measurement of the mass of the W boson in e+ e- collisions

A measurement of the mass of the W boson in hadronic e+e -> W+W- decays was performed with 183 pb-1 of data recorded with the OPAL detector at a centre-of-mass energy of s = 189 GeV. Using a one-dimensional reweighting technique where the W width is fixed to its Standard Model prediction, the mass was determined to M4q W = 80.360+-0.105stat. +- 0.093syst.GeV Furthermore, the influence of a reconstruction of W+W- > qq¯qq¯ (g) events as five jets on both the statistical and the systematic uncertainty was studied and optimised. It was also shown the feasibility of a two-dimensional analysis, a simultaneous fit to the two W masses of each event.