Probing Quantum Entanglement in $τ^+τ^-$ Pairs via the $ππ$ Channel at STCF

Abstract

Quantum entanglement and Bell-inequality violation in $τ^+τ^-$ pairs provide a sensitive probe of quantum correlations in high-energy interactions. We present a feasibility study of $e^+e^- \to τ^+τ^-$ at the proposed Super Tau-Charm Facility based on full Monte Carlo simulation at $\sqrt{s} = 7$ GeV, focusing on the $ππ$ channel ($τ^\pm \to π^\pmν$), which offers the maximal spin-analyzing power $|κ| = 1$ and the simplest final-state topology for validating the quantum-tomography framework. We establish a consistency chain from the tree-level QED prediction through truth-level and detector-level reconstruction, yielding a reconstructed concurrence of $0.279 \pm 0.007$ with the good-solution approach. A complementary full-simulation study of the $ρρ$ channel is also briefly reported. These results demonstrate that the STCF can provide a competitive platform for precision studies of quantum correlations in $τ$-lepton pairs.