On the new physics in Bhabha luminometry at future $e^+e^-$ colliders

TL;DR

This paper evaluates the potential impact of undiscovered new physics on Bhabha scattering used for luminosity measurement at future electron-positron colliders, proposing strategies to detect such effects.

Contribution

It assesses the theoretical uncertainties from potential new physics in Bhabha scattering and proposes asymmetry-based methods to constrain unknown heavy interactions.

Findings

New physics could significantly affect Bhabha scattering cross sections.

Asymmetries can be used to detect or constrain unknown heavy interactions.

Strategies are proposed for future colliders to improve luminosity precision.

Abstract

The absolute machine luminosity is a key quantity to achieve the high-precision physics program of future $e^+e^-$ collider. It is determined by measuring a theoretically well-known process, which, ideally, can be computed with arbitrary precision in the perturbation theory. However, yet undiscovered new physics could give a non-negligible contribution to the cross section of the luminosity monitoring process, thus invalidating the uncertainty determination of measured quantities. We assess the theoretical error of non-Standard Model origin to the small-angle Bhabha scattering in various future colliders scenarios. In addition, a possible running strategy to constrain unknown heavy interactions is proposed, relying on asymmetries that do not depend on the absolute luminosity.