2024/09/17 by A. Hayrapetyan, Aram Hayrapetyan, CMS Collaboration +2392 · 1 voice · 7 citations
Physics and Astronomy · Computer Science · #hep-ex
paper · pdf · doi:10.1103/physrevd.110.112016
Measurements of the polarization and spin correlation in top quark pairs (\mathrmtt) 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 \mathrmtt system and the top quark scattering angle in the \mathrmtt rest frame. The measured polarization and spin correlation are in agreement with the standard model. From the measured spin correlation, conclusions on the \mathrmtt spin entanglement are drawn by applying the Peres-Horodecki criterion. The standard model predicts entangled spins for \mathrmtt states at the production threshold and at high masses of the \mathrmtt system. Entanglement is observed for the first time in events at high \mathrmtt mass, where a large fraction of the \mathrmtt decays are space-like separated, with an expected and observed significance of above 5 standard deviations.