Measurement of Z/γ* production in compton scattering of quasi-real photons

The process \(e^+ e^- \to e^+ e^- Z/\gamma^*\) is studied with the OPAL detector at LEP at a centre of mass energy of \(\sqrt{s}\) = 189 GeV. The cross-section times the branching ratio of the Z/\(\gamma^*\) decaying into hadrons is measured within Lorentz invariant kinematic limits to be \((1.2 \pm 0.3 \pm 0.1)\) pb for invariant masses of the hadronic system between 5 GeV and 60 GeV and \((0.7 \pm 0.2 \pm 0.1)\) pb for hadronic masses above 60 GeV. The differential cross-sections of the Mandelstam variables \(\hat{s}, \hat{t}\), and \(\hatu\) 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 \({\rm e} \gamma\to{\rm e Z}/\gamma^*\) are derived.