Anomalous Zbb[over ¯] Couplings: From LEP to LHC.

Bin Yan,C.-P Yuan

doi:10.1103/physrevlett.127.051801

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 Zbb[over ¯] interactions through gg→Zh production at the LHC, which is sensitive to the axial-vector component of the Zbb[over ¯] couplings. The apparent degeneracy of the anomalous Zbb[over ¯] couplings implied by the LEP precision electroweak measurements seems to be resolved by the current 13TeV LHC Zh data, which is, however, dominated by the two data points with high transverse momentum of Z boson whose central values are in conflict with the standard model prediction. We also show the potential of the HL-LHC to either verify or exclude the anomalous Zbb[over ¯] couplings observed at LEP through measuring the Zh production rate at the HL-LHC, and this conclusion is not sensitive to the possible new physics contribution induced by top quark or Higgs boson anomalous couplings in the loop.

Highlights

Introduction.—The LEP and SLC experiments have measured the Z boson couplings and found most of the electroweak data are consistent with the standard model (SM) predictions with a remarkable precision [1]
Such a large discrepancy in AbFB could be evidence of new physics (NP) beyond the SM, it is important to exclude the possibility that it was caused by statistical fluctuation or some subtle systematic errors in experiments
In this Letter, we propose a novel method to probe the Zbbcouplings through the associated production of Z and the Higgs boson (h) via gg → Zh at the Large Hadron Collider (LHC)

Summary

Introduction

Introduction.—The LEP and SLC experiments have measured the Z boson couplings and found most of the electroweak data are consistent with the standard model (SM) predictions with a remarkable precision [1]. It shows that the HL-LHC measurements of the other processes, such as Ztt, htt, and hZZ, will mainly constrain all the anomalous couplings in Eq (1) except for κba.

Results

Conclusion