ATLAS Confirms Entanglement Between Z Bosons in Higgs Decays at 13 TeV

{"Researchers analyzed 139 fb⁻¹ of 13 TeV proton-proton collisions at the LHC, selecting Higgs events decaying to ZZ* with subsequent decays to electrons or muons. They reconstructed the spin density matrix of the Z pair from angular distributions of the leptons and quantified entanglement via a Bell inequality violation parameter exceeding classical bounds by more than 5 sigma. This extends prior observations from photons and trapped ions to particles with masses near 91 GeV and lifetimes below 10⁻²⁵ s.","The result strengthens the case that entanglement is not an artifact of low-energy laboratory conditions but persists at energies where electroweak symmetry breaking is directly probed. It connects to the 2024 top-quark entanglement measurement by the same collaboration and suggests that quantum information observables could become standard tools for characterizing new physics at colliders. Classical hidden-variable models are further constrained at scales relevant to early-universe cosmology.","Future runs at the High-Luminosity LHC will increase statistics by an order of magnitude, enabling differential measurements of entanglement as a function of invariant mass and tests against specific decoherence models. Integration with quantum-computing-inspired analysis pipelines could improve sensitivity to subtle beyond-Standard-Model effects in spin correlations."}