Bhabha scattering in the gauge-Higgs unification

TL;DR

This paper investigates the impact of $Z'$ bosons predicted by gauge-Higgs unification models on Bhabha scattering at future electron-positron colliders, highlighting potential deviations from the Standard Model and proposing new observables for detection.

Contribution

It provides the first detailed analysis of $Z'$ effects in gauge-Higgs unification models on Bhabha scattering and suggests new measurable observables at future colliders.

Findings

Deviations in differential cross sections are observable at 250 GeV.

Left-right asymmetries can be distinguished with polarized beams.

Small-angle Bhabha scattering remains a reliable luminosity measurement despite $Z'$ effects.

Abstract

We examine effects of $Z'$ bosons in gauge-Higgs unification (GHU) models at $\mathrm{e}^{+}\mathrm{e}^{-}\to \mathrm{e}^{+}\mathrm{e}^{-}$ Bhabha scatterings. We evaluate differential cross sections in Bhabha scatterings including $Z'$ bosons in two types of $\mathrm{SO}(5) \times \mathrm{U}(1) \times \mathrm{SU}(3)$ GHU models. We find that deviations of differential cross sections in the GHU models from those in the SM can be seen at $\sqrt{s} = 250\,\mathrm{GeV}$. With $80\%$-longitudinally polarized electron and $30\%$-longitudinally polarized positron beams, the left-right asymmetries in the GHU A- and B-models are resolved at more than $3\,\sigma$ at $L_{\rm int} =250\,\mathrm{fb}^{-1}$. We also show that Bhabha scattering with scattering angle less than 100 mrad can be safely used as luminosity measurements in $\mathrm{e}^{+}\mathrm{e}^{-}$ colliders since the effects of $Z'$ bosons are well suppressed for small scattering angle. We propose a new observable which can be measured at future TeV-scale $\mathrm{e}^{+} \mathrm{e}^{-}$ linear colliders.