Probing \(|V_{td}|\) in single-top production at \(pe^{\mp }\) colliders

Abstract

We study the consequences for top-quark physics of having electron and positron beams available at the LHeC and FCC-he, as was the case in HERA. We show that the asymmetry between top production in \(pe^+\) collisions and antitop production in \(pe^-\) reactions is sensitive to \(|V_{td}|\). By means of detailed parton-level Monte Carlo simulations of single t and \(\bar{t}\) production and its backgrounds, we parametrize the asymmetry dependence on \(|V_{td}|\) and estimate its uncertainties. Our analysis includes realistic phase-space cuts and machine-learning binary classifiers for background rejection. We thus obtain limits on \(|V_{td}|\) that are substantially stronger than current ones and also smaller than current projections for the HL-LHC. We have \(|V_{td}| < 1.6\times |V_{td}^{\textrm{PDG}}|\) at the LHeC, at 68% C.L. with \(L_{\textrm{int}}=2\)/ab.