An upper limit on the anomalous magnetic moment of the \tau lepton

TL;DR

This paper sets experimental upper limits on the anomalous magnetic and electric dipole moments of the tau lepton by analyzing Z^0 decay events collected at LEP, constraining physics beyond the Standard Model.

Contribution

First direct experimental limits on the tau lepton's anomalous magnetic and electric dipole form factors using LEP data, improving constraints on new physics.

Findings

Limit on F_2: -0.068 to 0.065 at 95% CL

Limit on electric dipole form factor: -3.8x10^-16 to 3.6x10^-16 e-cm

Analyzed 1429 tau gamma events from LEP data

Abstract

Using radiative Z^0 -> \tau^+ \tau^- \gamma events collected with the OPAL detector at LEP at \sqrt{s}= M_Z during 1990-95, a direct study of the electromagnetic current at the \tau\gamma vertex has been performed in terms of the anomalous magnetic form factor F_2 of the \tau lepton. The analysis is based on a data sample of 1429 e^+ e^- -> \tau^+ \tau^- \gamma events which are examined for a deviation from the expectation with F_2 = 0. From the non-observation of anomalous \tau^+ \tau^- \gamma production a limit of -0.068 < F_2 < 0.065 is obtained. This can also be interpreted as a limit on the electric dipole form factor F_3 as -3.8 x 10^-16 e-cm < eF_3 < 3.6 x 10^-16 e-cm. The above ranges are valid at the 95% confidence level.