Measurement of the W boson mass in the $W^{+}W^{-} \to qql \overline{\nu}$ channel with the OPAL detector at LEP

A new method to measure the mass of the W boson in the $W^{+}W^{-} \to qql \overline{\nu}$ channel, a convolution fit, was developed and applied to data recorded with the OPAL experiment at LEP. The Convolution method takes into account the precision of the measurement of each single event of the data sample in an unbinned maximum likelihood fit. The parent distribution of the likelihood fit includes a statistical description of the effects of Initial State Radiation on the mass reconstruction. An improvement of about 10% in the statistical error of the W mass measurement compared to other methods used within the OPAL collaboration is anticipated.