Probing Quantum Entanglement in $\tau^+\tau^-$ Pairs via the $\pi\pi$ Channel at STCF

TL;DR

This study explores the feasibility of probing quantum entanglement in tau lepton pairs at the proposed Super Tau-Charm Facility using Monte Carlo simulations, focusing on the $ au^ au$ pairs' $ ho ho$ and $ ext{pi} ext{pi}$ channels.

Contribution

It demonstrates that the STCF can effectively measure quantum correlations in tau pairs, establishing a framework for quantum tomography in high-energy physics.

Findings

Reconstructed concurrence of 0.279 ± 0.007 indicates measurable entanglement.

Full simulation confirms the viability of the $ ext{pi} ext{pi}$ channel for quantum correlation studies.

The study provides a baseline for future precision tests of quantum entanglement in tau pairs.

Abstract

Quantum entanglement and Bell-inequality violation in $\tau^+\tau^-$ pairs provide a sensitive probe of quantum correlations in high-energy interactions. We present a feasibility study of $e^+e^- \to \tau^+\tau^-$ at the proposed Super Tau-Charm Facility based on full Monte Carlo simulation at $\sqrt{s} = 7$ GeV, focusing on the $\pi\pi$ channel ($\tau^\pm \to \pi^\pm\nu$), which offers the maximal spin-analyzing power $|\kappa| = 1$ 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 $\rho\rho$ channel is also briefly reported. These results demonstrate that the STCF can provide a competitive platform for precision studies of quantum correlations in $\tau$-lepton pairs.