Measurement of the top-quark polarization and $t\bar{t}$ spin correlations with the CMS detector

We report a measurement of differential cross sections sensitive to top-quark polarization, t\bar{t} spin correlations, and angular correlations in dileptonic final states using proton-proton collision data collected by the CMS experiment during Run 2 of the LHC at 13 TeV. The two-lepton final state offers a clean environment in which the lepton angular distributions retain the spin information of the parent top quarks, allowing precise measurements of top-quark spin observables. All components of the spin-density matrix of the ttbar system are extracted multi-differentially in bins of the m_{t\bar{t}}, top-quark transverse momentum, and the top-quark scattering angle. Special attention is given to the production threshold region ($m_{t\bar{t}}<400\GeV$), where non-relativistic QCD binding effects, such as possible toponium formation, may affect the spin correlations. The results are unfolded to parton level and compared with Standard Model predictions, providing a stringent test of the top-quark spin dynamics and potential signs of physics beyond the Standard Model (BSM).