Measurements of the polarization and spin correlation in top quark pairs (tt¯) 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 √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 tt¯ system and the top quark scattering angle in the tt¯ rest frame. The measured polarization and spin correlation are in agreement with the standard model. From the measured spin correlation, conclusions on the tt¯ spin entanglement are drawn by applying the Peres-Horodecki criterion. The standard model predicts entangled spins for tt¯ states at the production threshold and at high masses of the tt¯ system. Entanglement is observed for the first time in events at high tt¯ mass, where a large fraction of the tt¯ decays are space-like separated, with an expected and observed significance of above 5 standard deviations.

Measurements of polarization and spin correlation and observation of entanglement in top quark pairs using lepton+jets events from proton-proton collisions at sqrt(s) = 13 TeV

Cavallo, N.;Fabozzi, F.;
2024-01-01

Abstract

Measurements of the polarization and spin correlation in top quark pairs (tt¯) 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 √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 tt¯ system and the top quark scattering angle in the tt¯ rest frame. The measured polarization and spin correlation are in agreement with the standard model. From the measured spin correlation, conclusions on the tt¯ spin entanglement are drawn by applying the Peres-Horodecki criterion. The standard model predicts entangled spins for tt¯ states at the production threshold and at high masses of the tt¯ system. Entanglement is observed for the first time in events at high tt¯ mass, where a large fraction of the tt¯ decays are space-like separated, with an expected and observed significance of above 5 standard deviations.
2024
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11563/201915
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