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arXiv:2511.17321

Parameter Inference from Final-State Entanglement in Higgs Decays

Jia Liu, Masanori Tanaka, Xiao-Ping Wang, Jing-Jun Zhang, Zifan Zheng

hep-phquant-phSubmitted Nov 21, 2025• Announced Nov 24, 2025• Revised Jul 26, 2026 (v2)
v1 · Nov 21, 2025v2 · Jul 26, 2026
arXivHTMLPDF

Abstract

The decay out-states of unstable Standard Model (SM) particles provide a unique, well-defined intrinsic quantum-information probe of the SM parameter space. We use Higgs decays as a test case: after tracing out kinematics, we compute entanglement among final-state spins and colors across all decay channels and impose a near-maximal entanglement-entropy criterion. This criterion yields quantitative indications for fundamental parameters. Within the SM, the entanglement entropy exhibits a global maximum close to the observed Higgs mass and the measured $W$ mass, the latter being equivalent to the $SU(2)_L$ gauge coupling. In a two-parameter kappa framework, applying the same criterion points to an SM-like balance between vector and fermion couplings, constraining the ratio of the sector-wide rescalings. These results suggest that entanglement extremality can serve as a complementary handle on fundamental parameters.

Journal reference
Phys. Rev. D 114, 015036 (2026)
DOI
10.1103/jynb-w9kq
Comments
17 pages, 7 figures, accepted for publication in PRD

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In this article, we study quantum entanglement properties of the three-body H→γllˉH\toγl\bar{l}H→γllˉ decays (for l=e,μ,τl=e,μ,τl=e,μ,τ) within the context of the Standard Model augmented with CP-violating interactions in the lepton Yukawa sector. Our aim is to elucidate the distribution of entanglement between the final photon, lepton and antilepton across the phase-space. These rare Higgs boson decays occur at 1-loop level, presenting a unique opportunity to scrutinize quantum correlations of fundamental interactions in tripartite systems by computing concurrence measures and investigating Bell non-locality. Moreover, we explore post-decay and autodistillation phenomena. Multipartite entanglement measures have much richer structure than those in the bipartite case, thus deserve more attention in collider phenomenology. In this line, we analyze here novel observables for these three-body Higgs boson decays, which can be extended to other multiparticle systems within the high-energy regime. We found that entanglement manifests among final particles, occasionally achieving a maximally entangled state in specific kinematical configurations. Also, these decay channels are promising for Bell non-locality tests but CP-effects are suppressed by lepton masses in this kind of observables.
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Measurements of ZZZ-boson pair entanglement in decays of Higgs bosons at the ATLAS experiment
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