Sensitivity Analysis of Singlet Vector-Like B Quarks via Photon-Induced Processes at FCC--$μp$

TL;DR

This paper assesses the sensitivity of a singlet vector-like B quark (VLQ-B) produced via photon-induced processes at a future FCC--$\mu$p collider with $\sqrt{s}=24.5~\mathrm{TeV}$. It employs a minimal effective Lagrangian with couplings $g^\$ and mixing $R_L$, focusing on the $B\to Zb$ decay with $Z\to \ell^+\ell^-$ and $W\to jj$ to form a clean final state and uses photon-proton EPA under the Narrow Width Approximation to compute cross sections, simulated with MadGraph5_aMC@NLO, MadSpin, and MadAnalysis5. The study derives $5\sigma$ discovery and 95% CL exclusion contours in the $g^*\,$–$M_B$ plane and finds that with $\mathcal{L}=1000~\mathrm{fb^{-1}}$ and $M_B=2$–$3$ TeV, discovery is possible for $g^*\approx 0.22$–$0.30$ and exclusion down to $g^*\approx 0.12$–$0.17$, significantly extending beyond current LHC reach. It further shows that higher luminosity enables sensitivity to smaller BR$(B\to Zb)$ values, and concludes that FCC--$\mu$p$ is a promising, complementary discovery platform for heavy VLQ searches, complementing ep and $e^+e^-$ colliders in the high-mass regime.

Abstract

This study presents a dedicated and systematic sensitivity analysis of a singlet-type vector-like $B$ quark at an FCC--$μp$ collider with a center-of-mass energy of $\sqrt{s}=24.5~\mathrm{TeV}$ via photon-induced production mechanisms. The analyses are based on the $B \to Zb$ decay and the lepton decay of the $Z$ boson on a clean and selective final state. In this regard, we observed that the applied kinematic cuts suppress the Standard Model backgrounds by several orders of magnitude while maintain high signal efficiency. Also, the obtained results show that for $\mathcal{L}=1000~\mathrm{fb^{-1}}$, even small coupling constant values in the mass range $M_B = 2$--$3$~TeV are accessible. In this context, an exclusion limit of $g^\ast \simeq 0.12$--$0.17$ at 95\% confidence level and a sensitivity in the range of $g^\ast \simeq 0.22$--$0.30$ for the $5σ$ discovery region are obtained. Moreover, the calculations indicate that scenarios with smaller ${\rm BR}(B\to Zb)$ values via increasing integrated luminosity values can be experimentally tested. As a result, the outputs of the study show that the FCC--$μp$ environment offers a unique and powerful discovery potential for vector-like quark searches that go beyond the current LHC limits and complement the decreasing sensitivity of the ep and $e^+e^-$ colliders in the high-mass regime. In this context, the findings suggest that the $μp$ colliders can be considered not only as a complementary option for the search of heavy new particles in the future accelerator programme, but also as a strategic discovery tool.

Figures (7)

• Figure 1: Tree-level Feynman diagrams for the photon-induced subprocesses $\gamma\,q\,(q=u,c)\to W^{+}B$.
• Figure 2: Production cross section of the photon-induced main process as a function of the vector-like $B$ quark mass for different values of the coupling parameter $g^\ast$.
• Figure 3: Distributions of the main kinematic variables used in the analysis for the signal and background processes.
• Figure 4: Expected $5\sigma$ discovery reach in the $g^\ast$--$M_B$ plane for integrated luminosities of $\mathcal{L}=400$ and $1000~\mathrm{fb^{-1}}$, considering the cases of $\delta=0$ and $\delta=10\%$.
• Figure 5: Expected $95\%$ confidence level exclusion contours in the $g^\ast$--$M_B$ plane for integrated luminosities of $\mathcal{L}=400$ and $1000~\mathrm{fb^{-1}}$ considering the cases of $\delta=0$ and $\delta=10\%$.