First Measurement of Z/gamma* Production in Compton Scattering of Quasi-real Photons

TL;DR

This paper reports the first measurement of Z/gamma* production via Compton scattering of quasi-real photons in electron-positron collisions, confirming theoretical predictions with experimental data.

Contribution

It provides the first experimental observation and measurement of Z/gamma* production in this specific scattering process at LEP energies.

Findings

Measured cross-section times branching ratio for Z/gamma* to hadrons: (0.9+-0.3+-0.1) pb for M_had > 60 GeV.

Measured cross-section times branching ratio for (e)egamma* production: (4.1+-1.6+-0.6) pb for 5 GeV < M_had < 60 GeV.

Results are consistent with Monte Carlo predictions from grc4f and PYTHIA.

Abstract

We report the first observation of Z/gamma* production in Compton scattering of quasi-real photons. This is a subprocess of the reaction e+e- to e+e-Z/gamma*, where one of the final state electrons is undetected. Approximately 55 pb-1 of data collected in the year 1997 at an e+e- centre-of-mass energy of 183 GeV with the OPAL detector at LEP have been analysed. The Z/gamma* from Compton scattering has been detected in the hadronic decay channel. Within well defined kinematic bounds, we measure the product of cross-section and Z/gamma* branching ratio to hadrons to be (0.9+-0.3+-0.1) pb for events with a hadronic mass larger than 60 GeV, dominated by (e)eZ production. In the hadronic mass region between 5 GeV and 60 GeV, dominated by (e)egamma* production, this product is found to be (4.1+-1.6+-0.6) pb. Our results agree with the predictions of two Monte Carlo event generators, grc4f and PYTHIA.