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arXiv:2603.28868

Higgs Boson Spookiness: Probing Quantum Nonlocality with Spacetime-Resolved $H\rightarrowτ^+τ^-$ Decays

Lawrence Lee, John Lawless, Caroline Riggall

hep-phhep-exquant-phSubmitted Mar 30, 2026• Announced Apr 1, 2026• 0 citations
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Abstract

We demonstrate that a future precision $ee$ Higgs factory would be able to perform a spacetime-resolved test of quantum nonlocality in Higgs boson decays. In simulated $ee\rightarrow ZH \rightarrow (μμ)(ττ)$ events at $\sqrt{s}=240$ GeV, we reconstruct $τ$ lepton decay vertices and measure spin correlations as a function of the spacetime interval between the two $τ$ decays. Such a measurement would be able to test Bell-inequality-violating correlations for spacelike-separated decays, enabling direct exclusion of superluminal, finite-speed entanglement signaling theories. With 0.75 ab$^{-1}$ of integrated luminosity, entanglement signal propagation speeds below $\approx2c$ can be excluded at 95$\%$ CL. Signals establishing any spin correlation can be excluded for speeds below $\approx9c$. This constitutes the first proposed spacetime-resolved measurement of electroweak quantum entanglement at a particle collider and demonstrates a unique capability of future Higgs factories.

Comments
6 pages, 3 figures

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