Beautiful Mirrors at the LHC

TL;DR

This work tackles the persistent $A^{b}_{FB}$ anomaly by proposing the Beautiful Mirrors model, which introduces vector-like quarks that mix with the bottom and shift its $Z$-couplings, thereby reconciling precision electroweak data while yielding testable LHC signatures. The authors analyze the exotic quark content—a $(3,2,-5/6)$ doublet containing $\omega$ and $\chi$, and a $(3,1,-1/3)$ state—focusing on how bottom-sector mixing affects Higgs and gauge couplings through a detailed mass-matrix framework and explicit mixing angles. They then study LHC phenomenology, emphasizing both pair and single production channels for the mirror quarks $b_2$, $b_3$, and $\chi$, with decays $b_{2,3}\to Zb$ or $hb$, and $\chi\to Wb$. For a representative mass point ($m_{b_2}\approx500$ GeV, $m_h=120$ GeV), they show that a 14 TeV LHC with 300 fb$^{-1}$ can establish the scenario and measure the key mixing parameter $s_R^2$ with about 20% precision, primarily through single production channels, while complementary processes confirm the overall doublet structure. These results demonstrate that the Beautiful Mirrors scenario is testable at the LHC and provide concrete strategies to extract the bottom-sector mixing that underpins the $A^{b}_{FB}$ solution.

Abstract

We explore the "Beautiful Mirrors" model, which aims to explain the measured value of $A^b_{FB}$, discrepant at the $2.9σ$ level. This scenario introduces vector-like quarks which mix with the bottom, subtly affecting its coupling to the $Z$. The spectrum of the new particles consists of two bottom-like quarks and a charge -4/3 quark, all of which have electroweak interactions with the third generation. We explore the phenomenology and discovery reach for these new particles at the LHC, exploring single mirror quark production modes whose rates are proportional to the same mixing parameters which resolve the $A_{FB}^b$ anomaly. We find that for mirror quark masses $\lesssim 500 GeV, a 14 TeV LHC with 300 {\rm fb}^{-1}$ is required to reasonably establish the scenario and extract the relevant mixing parameters.

Figures (2)

• Figure 1: The regions in the $Z$-$b$-$\overline{b}$ coupling parameter space favored by EW precision data. The inner (outer) shaded regions correspond to $1\sigma$ ($2\sigma$) agreement with the best fit shifts in the left- and right-handed couplings.
• Figure 2: Production cross sections for both single and pair production of mirror quarks, as a function of their masses and for the mixing angles specified in the text. The single $b_{2,3}$ + jets rates sum both production of $b_{2,3}$ + jets and $\overline{b}_{2,3}$ + jets. For this plot we have chosen $m_h = 120$ GeV