Hayrapetyan, A.Tumasyan, A.Adam, W.Andrejkovic, J. W.Benato, L.Bergauer, T.Druzhkin, D.2025-02-172025-02-17202412470-00102470-002910.1103/PhysRevD.110.1120162-s2.0-85214239868https://doi.org/10.1103/PhysRevD.110.112016Rossi Tisbeni, Simone/0000-0001-6776-285X; Acharya, Shriniketan/0009-0001-2997-7523; Gadallah, Mahmoud Moussa Abdelkhalek/0000-0002-8305-6661; Navarrete Ramos, Efren/0000-0002-5180-4020; Wardle, Nicholas/0000-0003-1344-3356; Giommi, Luca/0000-0003-3539-4313; Mousa, Jehad/0000-0002-2978-2718; Tytgat, Michael/0000-0002-3990-2074; Bakhshiansohi, Hamed/0000-0001-5741-3357Measurements 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/openAccessArticleQ1Q111011WOS:0014217950000020