A Measurement of the tau->electron Branching Ratio

TL;DR

This paper reports a precise measurement of the tau lepton's decay into an electron, tests lepton universality, and extracts the strong coupling constant alpha_s from tau decay data collected at LEP.

Contribution

It provides a new, highly precise measurement of the tau->electron branching ratio and uses this to test lepton universality and determine alpha_s at the Z0 scale.

Findings

Branching ratio for tau->e is 17.81% with small uncertainties.

Results support lepton universality in charged-current interactions.

Extracted alpha_s value is consistent with other measurements.

Abstract

The branching ratio for the decay tau->e nue nutau has been measured using Z0 decay data collected by the OPAL experiment at LEP. In total 33073 tau->e nue nutau candidates were identified from a sample of 186197 selected tau decays, giving a branching ratio of 17.81 +- 0.09(stat) +_ 0.06(sys)%. This result is combined with other measurements to test e-mu and mu-tau universality in charged-current weak interactions. Additionally, the strong coupling constant alpha_s has been extracted and evolved to the Z0 mass scale, giving alpha_s = 0.1204 +- 0.0011(exp) +- 0.0019(theory).