Hadronic photon-photon scattering at LEP

TL;DR

This paper reviews hadronic photon-photon interactions studied at LEP, highlighting areas of agreement and discrepancy between experimental results and perturbative QCD predictions, especially in high momentum and beauty production.

Contribution

It presents three new measurements of jet, hadron, and beauty production at LEP, expanding understanding of photon-photon hadronic processes and testing QCD predictions.

Findings

Good overall agreement between measurements and theory

Large discrepancies in high momentum particle and jet production

Open b-quark production exceeds theoretical predictions

Abstract

Hadronic interactions of two quasi-real photons have been studied extensively both during the LEP1 and the LEP2 data taking periods. The higher energies available at LEP2 in particular opened regions of phase space where hadronic processes can be predicted reliably by perturbative QCD calculations, usually available to next-to-leading order in the strong coupling constant for the process concerned. Over a wide range of observables and phase space good agreement is observed between measurements and theory, however, there are a few exceptions. The L3 collaboration has found large discrepancies for high momentum particle and jet production between theory and experiment, and measurements of open b-quark production by DELPHI, L3, and OPAL are consistently in excess of the theoretical values. Three new measurements have now become available and will be discussed in this paper: on jet and hadron production by OPAL and open beauty production by ALEPH.