Di-Jet Production in Photon-Photon colisions at sqrt(s)ee from 189 to 209 GeV

TL;DR

This paper investigates di-jet production in photon-photon collisions at LEP energies, measuring cross-sections, angular distributions, and jet structures, and compares results with QCD predictions and Monte Carlo models.

Contribution

It provides detailed measurements of di-jet cross-sections and angular distributions in photon-photon collisions, using multiple jet algorithms and exploring different phase space regions.

Findings

Quark and gluon processes dominate in different phase space regions.

Measured cross-sections agree with NLO QCD calculations within uncertainties.

Jet structures vary with the clustering algorithm used.

Abstract

Di-jet producion is studied in collisions of quasi-real photons at e+e- centre- of-mass energies sqrt(s)ee from 189 to 209 GeV at LEP. The data were collected with the OPAL detector. Jets are reconstructed using an inclusive k_t clustering algorithm for all cross-section measurements presented. A cone jet algorithm is used in addition to study the different structure of the jets resulting from either of the algorithms. The inclusive di-jet cross-section is measured as a function of the mean transverse energy Etm(jet) of the two leading jets, and as a functiuon of the estimated fraction of the photon momentum carried by the parton entering the hard sub-process, xg, for different regions of Etm (jet). Angular distribution in di-jet events are measured and used to demonstrate the dominance of quark and gluon initiated processes in different regions of phase space. Furthermore the inclusive di-jet cross-section as a function of |eta(jet)| and |delta eta (jet)| is presented where eta(jet) is the jet pseudo-rapidity. Different regions of the xg+ -xg- -space are explored to study and control the influence of an underlying event. The results are compared to next-to-leading order perturbative QCD calculations and to the predictions of the leading order Monte Carlo generator PYTHIA.