  In this letter it is shown how final-state QED corrections to the production
of a pair of resonances can distort the line shape of such a resonance in a
sizeable way. This effect depends on the definition of the line shape and can
reach up to 30%, depending on the final state. The mechanism is first displayed
for a particular case of ZZ production, for which an exact and approximate
treatment can be given. The approximate method is then applied to W-pair
production. In addition some simple rules of thumb are given for accurately
estimating the characteristic distortion effects, like the mass shift and peak
reduction.

High Energy Physics - Phenomenology