Measurements of Polarization and Spin Correlation and Observation of Entanglement in Top Quark Pairs Using Lepton Plus Jets Events From Proton-Proton Collisions at √s=13 Tev

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2024

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Amer Physical Soc

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Measurements 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.

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Rossi 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/0000-0001-5741-3357

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1

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110

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11

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