Interplay of beam polarisation and systematic uncertainties at future $e^+e^-$ colliders

TL;DR

This paper investigates how beam polarisation at future $e^+e^-$ colliders can help reduce and understand systematic uncertainties, complementing statistical improvements in electroweak measurements.

Contribution

It is the first study to evaluate the impact of beam polarisation on systematic uncertainties in electroweak precision tests at future colliders.

Findings

Beam polarisation can help isolate systematic effects.

Different polarisation configurations influence the precision of measurements.

Systematic uncertainties can be mitigated using polarisation strategies.

Abstract

Future high-energy $e^+e^-$ colliders will provide some of the most precise tests of the Standard Model. Statistical uncertainties on electroweak precision observables and triple gauge couplings are expected to improve by orders of magnitude over current measurements. This provides a new challenge in accurately assessing and minimising the impact of systematic uncertainties. Beam polarisation may hold a unique potential to isolate and determine the size of systematic effects. So far, studies have mainly focused on the statistical improvements from beam polarisation. This study aims to assess, for the first time, its impact on systematic uncertainties. A combined fit of precision observables, such as chiral fermion couplings and anomalous triple gauge couplings, together with experimental systematic effects is performed on generator-level differential distribution of 2-fermion and 4-fermion final-states. Different configurations of available beam polarisations and luminosities are tested with and without systematic effects, and will be discussed in the context of the existing projections on fermion and gauge boson couplings from detailed experimental simulations.