OFF-SHELL W-PAIR PRODUCTION IN E+E--ANNIHILATION - INITIAL-STATE RADIATION

With a current-splitting technique, we calculate the gauge-invariant initial-state radiation to order 0(alpha) with soft-photon exponentiation for on- and off-shell W-pair production. This result generalizes the convolution formula, which is known from the description of the Z resonance, to the case of the production of two W-bosons. After up to eightfold analytical integrations, a sufficiently smooth integral over three invariant masses remains to be treated numerically. Including the Coulomb singularity, the largest corrections are covered. We discuss the corrections in a large energy range up to square-root s = 1 TeV and draw numerical conclusions on their influence on the W-mass determination at LEP 200.