Model-independent measurement of the top quark polarisation

TL;DR

This paper proposes a new asymmetry measurement in top quark decay that allows for a model-independent determination of top quark polarisation across various collider experiments, leveraging existing W helicity fraction data.

Contribution

The paper introduces a novel asymmetry in top decay that directly relates to top polarisation and can be used independently of specific production models.

Findings

The asymmetry is proportional to top polarisation and known W helicity fractions.

It enables model-independent top polarisation measurements at colliders.

The method utilizes existing precise measurements of W helicity fractions.

Abstract

We introduce a new asymmetry in the decay t -> W b -> l nu b, which is shown to be directly proportional to the polarisation of the top quark along a chosen axis, times a sum of W helicity fractions. The latter have already been precisely measured at the Tevatron and the Large Hadron Collider. Therefore, this new asymmetry can be used to obtain a model-independent measurement of the polarisation of top quarks produced in any process at hadron or lepton colliders.