The anomalous $Zb\bar{b}$ couplings: From LEP to LHC

TL;DR

This paper introduces a new method using $Zh$ production at the LHC to investigate anomalous $Zb\bar{b}$ couplings, potentially resolving longstanding discrepancies from LEP data and testing new physics scenarios.

Contribution

It proposes a novel approach to probe $Zb\bar{b}$ interactions via $gg\to Zh$ production at the LHC, sensitive to axial-vector couplings, and demonstrates its effectiveness with current and future collider data.

Findings

Current 13 TeV LHC data can resolve LEP anomalies.

$Zh$ production rate measurements can confirm or exclude anomalous couplings.

Results are robust against top/Higgs loop contributions.

Abstract

The bottom quark forward-backward asymmetry ($A_{FB}^b$) data at LEP exhibits a long-standing discrepancy with the standard model prediction. We propose a novel method to probe the $Zb\bar{b}$ interactions through $gg\to Zh$ production at the LHC, which is sensitive to the axial-vector component of the $Zb\bar{b}$ couplings. We demonstrate that the $Zh$ data collected at the 13 TeV LHC can already resolve the apparent degeneracy of the anomalous $Zb\bar{b}$ couplings implied by the LEP precision electroweak measurements, with a strong dependence on the observed distribution of the $Z$ boson transverse momentum. We also show the potential of the HL-LHC to either verify or exclude the anomalous $Zb\bar{b}$ couplings observed at LEP through measuring the $Zh$ production rate at the HL-LHC, and this conclusion is not sensitive to possible new physics contribution induced by top quark or Higgs boson anomalous couplings in the loop.