Hayrapetyan, A.Tumasyan, A.Adam, W.Andrejkovic, J. W.Benato, L.Bergauer, T.Chatterjee, S.2025-03-232025-03-2320242470-00102470-0029https://doi.org/10.1103/PhysRevD.110.112016https://hdl.handle.net/11486/5563Measurements of the polarization and spin correlation in top quark pairs (t (t) over bar) are presented using events with a single electron or muon and jets in the final state. The measurements are based on proton-proton collision data from the LHC at root s = 13 TeV collected by the CMS experiment, corresponding to an integrated luminosity of 138 fb(-1). All coefficients of the polarization vectors and the spin correlation matrix are extracted simultaneously by performing a binned likelihood fit to the data. The measurement is performed inclusively and in bins of additional observables, such as the mass of the t (t) over bar system and the top quark scattering angle in the t (t) over bar rest frame. The measured polarization and spin correlation are in agreement with the standard model. From the measured spin correlation, conclusions on the t (t) over bar spin entanglement are drawn by applying the Peres-Horodecki criterion. The standard model predicts entangled spins for t (t) over bart states at the production threshold and at high masses of the t (t) over bart system. Entanglement is observed for the first time in events at high t (t) over bar mass, where a large fraction of the t (t) over bar decays are spacelike separated, with an expected and observed significance of above 5 standard deviations.eninfo:eu-repo/semantics/openAccessArticle1101110.1103/PhysRevD.110.1120162-s2.0-85214239868Q1WOS:001421795000002Q1