Tests of the Standard Model and Constraints on New Physics from Measurements of Fermion-pair Production at 130-172 GeV at LEP

TL;DR

This paper reports measurements of fermion-pair production at LEP energies, testing the Standard Model and setting limits on new physics through cross-sections, asymmetries, and searches for beyond Standard Model particles.

Contribution

It provides new precise measurements of fermion-pair production and constraints on extensions of the Standard Model using LEP data at 130-172 GeV.

Findings

Measured cross-sections and asymmetries consistent with Standard Model

Improved limits on four-fermion contact interactions

Constraints on chargino and gluino production

Abstract

Production of events with hadronic and leptonic final states has been measured in e^+e^- collisions at centre-of-mass energies of 130-172 GeV, using the OPAL detector at LEP. Cross-sections and leptonic forward-backward asymmetries are presented, both including and excluding the dominant production of radiative Z \gamma events, and compared to Standard Model expectations. The ratio R_b of the cross-section for bb(bar) production to the hadronic cross-section has been measured. In a model-independent fit to the Z lineshape, the data have been used to obtain an improved precision on the measurement of \gamma-Z interference. The energy dependence of \alpha_em has been investigated. The measurements have also been used to obtain limits on extensions of the Standard Model described by effective four-fermion contact interactions, to search for t-channel contributions from new massive particles and to place limits on chargino pair production with subsequent decay of the chargino into a light gluino and a quark pair.