Measurements of polarization and spin correlation and observation of entanglement in top quark pairs using ; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>lepton</mml:mi><mml:mo>+</mml:mo><mml:mtext>jets</mml:mtext></mml:mrow></mml:math>; events from proton-proton collisions at ; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msqrt><mml:mi>s</mml:mi></mml:msqrt><mml:mo>=</mml:mo><mml:mn>13</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>TeV</mml:mi></mml:math> | CU Experts

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 spacelike separated, with an expected and observed significance of above 5 standard deviations.; ; ; ; ; © 2024 CERN, for the CMS Collaboration; 2024; CERN; ; ;

Hayrapetyan A; Tumasyan A; Adam W; Andrejkovic JW; Benato L; Bergauer T; Chatterjee S; Damanakis K; Dragicevic M; Hussain PS

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