Tests of the Standard Model and Constraints on New Physics from Measurements of Fermion-pair Production at 189 GeV at LEP

TL;DR

This paper reports measurements of fermion-pair production at 189 GeV at LEP, testing the Standard Model and setting limits on new physics including contact interactions, heavy particles, and extra dimensions.

Contribution

It provides precise cross-section and angular distribution measurements at 189 GeV and uses them to constrain new physics models beyond the Standard Model.

Findings

Measured energy dependence of alpha_em

Set limits on four-fermion contact interactions

Constrained models with extra dimensions

Abstract

Cross-sections and angular distributions for hadronic and lepton pair final states in e+e- collisions at a centre-of-mass energy near 189 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. The results are used to measure the energy dependence of the electromagnetic coupling constant alpha_em, and to place limits on new physics as described by four-fermion contact interactions or by the exchange of a new heavy particle such as a sneutrino in supersymmetric theories with R-parity violation. A search for the indirect effects of the gravitational interaction in extra dimensions on the mu+mu- and tau+tau- final states is also presented.