Feasibility Study of $e^+e^-\to \eta_cJ/\psi$ Production and Fully-Charmed Tetraquark Searches at STCF

Abstract

The proposed high-luminosity Super Tau-Charm Facility (STCF) offers a clean experimental environment for threshold studies of exotic hadrons. In this Letter, we evaluate the expected significance for the fully-charmed vector tetraquark candidate $T_{4c}$ in the $e^+e^- \to \eta_c J/\psi$ channel at the STCF. Using Monte Carlo simulations of an energy scan from $\sqrt{s}=6.71$ to $6.79~\mathrm{GeV}$ with $100~\mathrm{fb}^{-1}$ per point, we adopt a high-efficiency single-tag (ST) reconstruction of $J/\psi$ leptonic decays as the primary strategy, with a double-tag (DT) reconstruction of $\eta_c \to K^+K^-\pi^0$ retained as an independent cross-check. Because the signal cross section is governed by the still-uncertain dielectron width $\Gamma_{ee}$, we consider three benchmark hypotheses, $\Gamma_{ee}=0.25, 0.5, 1~\mathrm{eV}$. The corresponding expected ST significances are $5.1\,\sigma$, $10.6\,\sigma$, and $20.5\,\sigma$, respectively. These results indicate that the STCF can provide meaningful sensitivity to fully-charmed tetraquark states near threshold.