Observation of quantum entanglement in top quark pair production in proton-proton collisions at $\sqrt{s}$ = 13 TeV

CMS Collaboration

Preprint

PUBDB-2024-05186

Observation of quantum entanglement in top quark pair production in proton-proton collisions at $\sqrt{s}$ = 13 TeV

CMS Collaboration (Collaboration author)DESY*

2024

[10.3204/PUBDB-2024-05186]

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Please use a persistent id in citations: doi:10.3204/PUBDB-2024-05186

Report No.: CERN-EP-2024-137; CMS-TOP-23-001; arXiv:2406.03976

Abstract: Entanglement is an intrinsic property of quantum mechanics and is predicted to be exhibited in the particles produced at the Large Hadron Collider. A measurement of the extent of entanglement in top quark-antiquark ($\mathrm{t\bar{t}}$) events produced in proton-proton collisions at a center-of-mass energy of 13 TeV is performed with the data recorded by the CMS experiment at the CERN LHC in 2016, and corresponding to an integrated luminosity of 36.3 fb$^{-1}$. The events are selected based on the presence of two leptons with opposite charges and high transverse momentum. An entanglement-sensitive observable $D$ is derived from the top quark spin-dependent parts of the $\mathrm{t\bar{t}}$ production density matrix and measured in the region of the $\mathrm{t\bar{t}}$ production threshold. Values of $D\lt-$1/3 are evidence of entanglement and $D$ is observed (expected) to be $-$0.480$^{+0.026}_{-0.029}$ ($-$0.467$^{+0.026}_{-0.029}$) at the parton level. With an observed significance of 5.1 standard deviations with respect to the non-entangled hypothesis, this provides observation of quantum mechanical entanglement within $\mathrm{t\bar{t}}$ pairs in this phase space. This measurement provides a new probe of quantum mechanics at the highest energies ever produced.

Keyword(s): p p: colliding beams ; top: pair production ; p p: scattering ; spin: dependence ; quantum mechanics: entanglement ; threshold: production ; entanglement: quantum ; Bell inequality ; lepton: transverse momentum ; transverse momentum: high ; CERN LHC Coll ; CMS ; CERN Lab ; density matrix ; lepton: pair production ; final state: ((n)jet dilepton) ; parton ; quark antiquark ; phase space ; experimental results ; 13000 GeV-cms