Measurement of Z/γ* Production in Compton Scattering of Quasi-Real Photons

The process e⁺e^- → e⁺e^-Z/γ* is studied with the OPAL detector at LEP at a centre of mass energy of √ {s} = 189 GeV. The cross-section times the branching ratio of the Z/γ* decaying into hadrons is measured within Lorentz invariant kinematic limits to be (1.2±0.3±0.1) pb for invariant masses of the hadronic system between 5 GeV and 60 GeV and (0.7±0.2±0.1) pb for hadronic masses above 60 GeV. The differential cross-sections of the Mandelstam variables hat {s}, hat {t}, and hat {u} are measured and compared with the predictions from the Monte Carlo generators grc4f and PYTHIA. From this, based on a factorisation ansatz, the total and differential cross-sections for the subprocess eγ → eZ/γ* are derived.