2026/07/16 by ShivaSankar K. A., Arindam Das, Sanjoy Mandal
#hep-ph
We study quantum spin correlations in top-quark pair production at future lepton colliders in the presence of a neutral gauge boson from anomaly-free general U(1) extensions of the Standard Model. The process ℓ+ℓ-→ t t, with ℓ=e,μ, is analyzed through the spin-density matrix including γ, Z and Z^′ exchange and their interference. We focus on quantum-information observables such as the sufficient entanglement marker Dmin, concurrence, purity and the maximal Clauser-Horne-Shimony-Holt (CHSH) parameter, and compare their behavior with conventional rate information. Within the U(1)X framework, we consider several representative charge assignments to investigate how different chiral structures influence these observables, with particular emphasis on the Z^′ resonance region and polarized e-e+ collisions, where the two allowed initial-state helicity configurations can be selectively enhanced. We show that electron-beam polarization provides a direct handle on the left- and right-handed lepton charges of various U(1)X scenarios. These results demonstrate that quantum spin observables provide information complementary to cross sections and angular distributions in searches for chiral neutral gauge interactions.