Final-state radiation and line-shape distortion in resonance pair production

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 an given for accurately estimating the characteristic distortion effects, like the mass shift and peak reduction. (C) 1998 Elsevier Science B.V. All rights reserved.