Isolating systematic effects with beam polarisation at $e^+e^-$ colliders

TL;DR

This paper explores how beam polarisation at future $e^+e^-$ colliders can help isolate and quantify systematic uncertainties, enhancing the precision of Standard Model tests by combining systematic and electroweak fits.

Contribution

It develops a framework for fitting systematic effects alongside electroweak observables using beam polarisation configurations, demonstrating initial tests with muon acceptance systematic effects.

Findings

Beam polarisation can help distinguish systematic uncertainties from physical effects.

A combined fit framework for systematics and electroweak observables is established.

Initial tests show consistent results in fitting luminosity, polarisation, and systematic effects.

Abstract

Future high-energy $e^+e^-$ colliders will provide some of the most precise tests of the Standard Model. Statistical uncertainties are expected to improve by orders of magnitude over current measurements. This provides a new challenge in accurately assessing and minimizing systematic uncertainties. Beam polarisation may hold a unique potential to isolate and determine the size of systematic effects. This study aims to set this hypothesis by setting up a combined fit of systematic effect and electroweak observables that can test different configurations of available beam polarisations and luminosities. A framework for this fit is developed. In a first test it fits the luminosity and polarisation with external constraints to 2-fermion and 4-fermion differential distributions. An implementation of a first systematic - the muon acceptance - shows consistent behaviour in this framework. This lays the groundwork for testing the interplay of systematic and physical effects in the presence or absence of beam polarisation.