Measurement of the W boson mass using large rapidity electrons

\We present a measurement of the W bosonmass using data collected by the DO experiment at the Fermilab Tevatronduring 1994-1995. We identify W bosonsby their decays to ev final states where the electron is detected in a forward calorimeter. We extract the W bosonmass M-W by fitting the transverse massand transverse electron and neutrino momentum spectra from a sample of 11 089 W-->e nu decay candidates. We use a sample of 1687 dielectron events, mostly due to Z-->ee decays, to constrain our model of the detector response. Using the forward calorimeterdata, we measure M-w=80.691+/-0.227 GeV. Combining the forward calorimetermeasurements with our previously published central calorimeterresults, we obtain M-W= 80.482 +/-0.091 GeV.