Measurements of the polarization and spin correlation in top quark pairs ((Formula presented)) 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 (Formula presented) collected by the CMS experiment, corresponding to an integrated luminosity of (Formula presented). 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 (Formula presented) system and the top quark scattering angle in the (Formula presented) rest frame. The measured polarization and spin correlation are in agreement with the standard model. From the measured spin correlation, conclusions on the (Formula presented) spin entanglement are drawn by applying the Peres-Horodecki criterion. The standard model predicts entangled spins for (Formula presented) states at the production threshold and at high masses of the (Formula presented) system. Entanglement is observed for the first time in events at high (Formula presented) mass, where a large fraction of the (Formula presented) decays are spacelike 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 √s=13  TeV

Alexe, C.;Bruschini, D.;
2024

Abstract

Measurements of the polarization and spin correlation in top quark pairs ((Formula presented)) 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 (Formula presented) collected by the CMS experiment, corresponding to an integrated luminosity of (Formula presented). 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 (Formula presented) system and the top quark scattering angle in the (Formula presented) rest frame. The measured polarization and spin correlation are in agreement with the standard model. From the measured spin correlation, conclusions on the (Formula presented) spin entanglement are drawn by applying the Peres-Horodecki criterion. The standard model predicts entangled spins for (Formula presented) states at the production threshold and at high masses of the (Formula presented) system. Entanglement is observed for the first time in events at high (Formula presented) mass, where a large fraction of the (Formula presented) decays are spacelike separated, with an expected and observed significance of above 5 standard deviations.
2024
Settore PHYS-01/A - Fisica sperimentale delle interazioni fondamentali e applicazioni
Top quark; Polarization; Hadron colliders
   Advanced Multi-Variate Analysis for New Physics Searches at the LHC
   AMVA4NewPhysics
   European Commission
   Horizon 2020 Framework Programme
   675440

   Search for Higgs bosons decaying to charm quarks
   HIGCC
   European Commission
   Horizon 2020 Framework Programme
   724704

   Direct and indirect searches for new physics in events with top quarks using LHC proton-proton collisions at the CMS detector
   LHCTOPVLQ
   European Commission
   Horizon 2020 Framework Programme
   752730

   Majorana neutrino discovery strategy with CMS
   MajorNet
   European Commission
   Horizon 2020 Framework Programme
   758316

   International Training Network for Statistics in High Energy Physics and Society
   INSIGHTS
   European Commission
   Horizon 2020 Framework Programme
   765710

   The strong interaction at the frontier of knowledge: fundamental research and applications
   STRONG-2020
   European Commission
   Horizon 2020 Framework Programme
   824093

   INnovative TRiggEr techniques for beyond the standard model PhysIcs Discovery at the LHC
   INTREPID
   European Commission
   Horizon Europe Framework Programme
   101115353

   Fundamental properties and time-scan of QCD matter at high densities and temperature exposed by jet substructure in heavy ion collisions with CMS experiment at the LHC
   QCDHighDensityCMS
   European Commission
   Horizon 2020 Framework Programme
   101002207
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11384/154948
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