Impact of Colliding Beams Helicity on the Production of Leptoquarks and Collider Experimental Parameters

TL;DR

This work investigates how beam helicity at future linear colliders can optimize the production and study of vector leptoquarks (VLQs) by exploiting polarized $e^{-}e^{+}$ collisions and contrasting with photon-initiated channels. Using a UV-complete model featuring a vector leptoquark $U_1^\mu$, a color-octet $G'^\mu$, a neutral $Z'^\mu$, and vector-like fermions, the authors quantify cross sections, left-right asymmetries, and effective luminosities under realistic polarization scenarios. They find a maximal VLQ-pair production cross section of about $\sigma \approx 120$ fb at $\sqrt{s}=3$ TeV for favorable polarizations, with effective luminosity ratios up to $L_{\text{eff}}/L \approx 0.90$–$0.95$ and $A_{LR}$ reaching $0.16$ under full polarization, providing powerful discriminants of chiral couplings. These results map explicit polarization configurations that maximize discovery reach and minimize systematics, highlighting the critical role of beam helicity in future high-energy $e^{-}e^{+}$ colliders for VLQ searches and flavor-physics connections.

Abstract

Vector Leptoquarks (VLQs) have emerged as primary candidates for resolving discrepancies in the Standard Model, specifically within $B$-meson decay channels and the anomalous magnetic moment of the muon. This work presents a rigorous evaluation of VLQ pair production across $e^{-}e^{+}$ collision modes at future linear colliders with center-of-mass energies ranging from 14~TeV to 100~TeV. Our analysis demonstrates that longitudinal beam polarization is a transformative tool for enhancing signal sensitivity. We find that $e^{-}e^{+}$ annihilation consistently yields superior cross-sections compared to photon fusion processes across a mass range of 500--3000~GeV. By optimizing beam helicity to specific configurations, such as $P_{e^{-}} = -0.8$ and $P_{e^{+}} = +0.6$, the production cross-section can be maximized to 120~fb at $\sqrt{s} = 3$~TeV. We further establish that the Left-Right Asymmetry ($A_{LR}$) serves as a robust discriminator for the chiral structure of new physics, peaking at 0.16 under full polarization. Additionally, we show that effective luminosity can be enhanced to 95\% of the total luminosity, while high polarization degrees significantly suppress relative uncertainties in the effective polarization. These results provide a quantitative roadmap for optimizing discovery potential and minimizing systematic errors in future high-energy physics experiments.

Figures (6)

• Figure 1: Mass vs Cross section with e- e+ Collider.
• Figure 2: Comparison of cross sections for $e^- e^+ \rightarrow \text{VLQ}\,\bar{\text{VLQ}}$ and $\gamma \gamma \rightarrow \text{VLQ}\,\bar{\text{VLQ}}$ processes at different center-of-mass energies.
• Figure 3: Contour plot of cross section versus polarization for $e^{+} e^{-} \rightarrow \text{LQ} \,\bar{\text{LQ}}$ at 3 TeV.
• Figure 4: Contour plot of the asymmetry ratio $A_{LR}$ for $e^{+} e^{-} \rightarrow \text{LQ} \,\bar{\text{LQ}}$ as a function of electron and positron polarizations at 3 TeV.
• Figure 5: (a) and (b) show the effective luminosity ratio ($L_{\text{eff}}/L$) versus electron beam polarization ($P_{e^-}$) for different positron polarization configurations.