Spin correlations and quantum entanglement in $\gamma \gamma \to t\bar{t}$ at polarized photon colliders with NLO QCD corrections

Abstract

We study spin correlations and quantum entanglement in the process $\gamma \gamma \to t\bar{t}$ with the photons coming from Compton backscattered laser beam. We present predictions for the cross sections and spin observables including next-to-leading order (NLO) QCD corrections under various beam-polarization configurations. The NLO QCD corrections significantly enhance the total cross section while having only a minor impact on spin observables. Using the spin density matrix of the $t\bar{t}$ system, we further investigate quantum entanglement and Bell nonlocality. We find that the entanglement is the strongest near the $t\bar{t}$ invariant-mass threshold, while both entanglement and Bell nonlocality are highly sensitive to the initial beam polarization. Our results provide a theoretical basis for future studies of quantum correlations in top-quark pair production at photon colliders.

Comments: 14 pages, 3 figures