Complementary constraints on $Zb\bar{b}$ couplings at the LHC

TL;DR

This paper introduces a novel LHC-based method to precisely measure the $Zb\bar{b}$ couplings by analyzing charge asymmetries in $Z$ boson production with $b$-jets, leveraging interference effects and high-luminosity data.

Contribution

It proposes a new charge asymmetry technique at the LHC to directly probe $Zb\bar{b}$ couplings, surpassing previous limitations of LEP measurements.

Findings

Potential to reject wrong-sign right-handed coupling at 4σ with current capabilities.

Enhanced charge-tagging could increase discrimination to 6σ.

Utilizes interference effects between $Z$ and photon amplitudes.

Abstract

We propose a new strategy to probe the $Z$ boson couplings to bottom and charm quarks at the LHC. In this work we mainly focus on the case of bottom quarks. Here, the $Z$ boson is produced in association with two $b$-jets and decays to electrons or muons. In this final state, tagging the charge of the $b$-jets allows us to measure the charge asymmetry and thus to directly probe the $Zb\bar{b}$ couplings. The leptonic final state not only allows us to cleanly reconstruct the $Z$ boson but also to mitigate the otherwise overwhelming backgrounds. Furthermore, while LEP could only scan a limited range of dilepton invariant masses, there is no such limitation at the LHC. Consequently, this allows us to make full use of the interference between the amplitudes mediated by a $Z$ boson and a photon. Using the full high-luminosity LHC dataset of $3~\text{ab}^{-1}$ and with the current flavor and charge-tagging capabilities would allow us to reject the wrong-sign right-handed coupling solution by 4$\sigma$. Further improving the charge-tagging efficiency would disfavor it by 6$\sigma$.