Measurement of Z/gamma* production in Compton scattering of quasi-real photons

TL;DR

This paper measures the production cross-sections of Z/gamma* in quasi-real photon Compton scattering at LEP, comparing experimental results with Monte Carlo predictions and deriving subprocess cross-sections.

Contribution

It provides the first detailed measurement of Z/gamma* production in this process at LEP and compares results with theoretical models, extracting subprocess cross-sections.

Findings

Measured cross-sections for Z/gamma* production at different hadronic mass ranges.

Compared differential cross-sections with Monte Carlo predictions.

Derived subprocess cross-sections using a factorisation approach.

Abstract

The process e+ e- -> 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 +/- 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 s-hat, t-hat, and u-hat 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 e gamma -> e Z/gamma* are derived.