Spin correlations and Bell nonlocality in $ \Lambda \overline{\Lambda} $ pair production from e+e− collisions with a thrust cut

A bstract: We present a comprehensive theoretical study of spin correlations in $$ \Lambda \overline{\Lambda} $$ Λ Λ ¯ production from e ⁺ e ⁻ annihilation, providing the theoretical predictions for the Belle II experiment. Using soft-collinear effective theory, we perform the first resummation of large logarithms for the longitudinal ( C _LL ) and transverse ( C _TT ) spin correlations for events with a cut on the thrust variable. Our calculation achieves next-to-next-to-leading logarithmic accuracy and incorporates the determination of polarized fragmenting jet functions. This framework provides robust predictions with significantly reduced theoretical uncertainties compared to fixed-order parton model approaches. Furthermore, we establish a direct mapping between the experimentally accessible spin correlation, C _TT , and a testable CHSH-Bell inequality. This result reframes C _TT as a quantitative probe of quantum decoherence, providing a novel tool to measure the degree of parton-level entanglement that survives the fragmentation and hadronization process.