Measurement of W Polarisation at LEP

TL;DR

This paper measures the polarization states of W bosons produced at LEP across various energies, confirming the Standard Model prediction for the fraction of longitudinally polarized W bosons.

Contribution

It provides the first detailed measurement of W boson polarization states at LEP energies, including their dependence on production angle.

Findings

Measured the fraction of longitudinal W bosons as 0.218 ± 0.027 ± 0.016.

Confirmed agreement with Standard Model predictions.

Analyzed polarization dependence on production angle.

Abstract

The three different helicity states of W bosons produced in the reaction e+ e- -> W+ W- -> l nu q q~ at LEP are studied using leptonic and hadronic W decays. Data at centre-of-mass energies \sqrt s = 183-209 GeV are used to measure the polarisation of W bosons, and its dependence on the W boson production angle. The fraction of longitudinally polarised W bosons is measured to be 0.218 \pm 0.027 \pm 0.016 where the first uncertainty is statistical and the second systematic, in agreement with the Standard Model expectation.