The Measurement of M(W) from the W+W- Threshold Cross Section at LEP2

The rapid increase of the e+e- --> W+W- cross section in the threshold region provides a method for measuring M(W) at LEP2. The dependence of the theoretical cross section – including the effects of the finite W width, Coulomb interactions and initial state radiation – on the collider energy and on the mass and width of the W is investigated in order to deduce the optimal collider energy which maximizes the sensitivity to M(W). Statistical and systematic uncertainties are studied in detail. The background contribution from QCD four-jet production is estimated. It is shown that by running LEP2 at a collision energy of approximately 161 GeV and obtaining a luminosity of order 100 inverse picobarns per experiment, an uncertainty on the measured value of M(W) of ±70 MeV should be achievable.