Exploring the $t\bar{t}$ threshold at an electron-positron collider

Abstract

Future electron-positron colliders offer a unique opportunity for high-precision measurements of the top-quark mass, width, strong coupling constant, and top-quark Yukawa coupling via a scan of the $t\bar{t}$ threshold. We present the first prospect study of the simultaneous determination of these parameters, incorporating the latest reference detector design for the Circular Electron-Positron Collider (CEPC). We find that the precision of the top-quark mass measurement can reach a few MeV excluding the theoretical uncertainty on the cross-section, which is nearly two orders of magnitude better than the high-luminosity LHC (HL-LHC) projections. The current theoretical uncertainty of the cross-section calculation is the limiting factor.

Figures (4)

• Figure 1: The $t\bar{t}\xspace$ cross-section near threshold as a function of $\sqrt{s}\xspace$, shown at N$^3$LO, with ISR, and with ISR+LS effects.
• Figure 2: Normalized Fisher information for $m_{\text{t}}\xspace$, $\Gamma_{\text{t}}\xspace$, $\alpha_{\text{S}}\xspace$ and $y_{\text{t}}\xspace$ as a function of $\sqrt{s}\xspace$, based on N$^3$LO+ISR+LS cross-section.
• Figure 3: Two-dimensional likelihood scan over $m_{\text{t}}$ and $\Gamma_{\text{t}}$ with full systematic uncertainties except the theoretical one from the $t\bar{t}$ cross-section calculation, in the BASE scenario using 5 energy points with 56 $\text{fb}^{-1}$ per point.
• Figure 4: Two-dimensional likelihood scan over $m_{\text{t}}$ and $\Gamma_{\text{t}}$ with full systematic uncertainties except the theoretical one from the $t\bar{t}$ cross-section calculation, in the EXT scenario using 5 energy points with 84 $\text{fb}^{-1}$ per point.