Spin Analysis of the Process e+e- --> tau+tau- at LEP

TL;DR

This paper reports precise measurements of tau lepton polarization and spin correlations at LEP, confirming Standard Model predictions and determining the weak mixing angle with high accuracy.

Contribution

It provides the first precise measurement of tau polarization and spin correlations at LEP, and determines the effective weak mixing angle assuming lepton universality.

Findings

Measured tau polarization and spin correlations are consistent with Standard Model.

Determined the weak mixing angle as sin^2(theta_W) = 0.2325 +- 0.0006.

Results support lepton universality in neutral current interactions.

Abstract

Using the data collected by the four experiments at LEP during 1990-1994, a precise measurement of the tau longitudinal polarisation (P_tau) has been performed, as well as the measurement of the transverse-transverse and transverse-normal tau spin correlations. From the P_tau measurement, assuming lepton universality of the neutral currents, the effective weak mixing angle has been determined to be sin(theta_W) = 0.2325 +- 0.0006. The Standard Model predictions are consistent with the measured results.