Studies of e+e- -> Zgamma -> mu+ mu- gamma events at sqrt{s} = 189-208 GeV

Radiative returns to the Z peak decaying to muon pairs are selected at 189 to 208 GeV centre-of-mass energies, and event kinematic variables are analysed . The results are interpreted in terms of a possible bias of the Z mass peak position, or of a shift in the LEP centre-of-mass energy, yielding Delta mZ = +209 +- 79 MeV (stat.) +- 35 MeV (syst.) with 94% chi-square probability, Delta E(LEP) = -334 +- 182 MeV (stat.) +- 96 MeV (syst.) with 14% chi-square probability.