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arXiv · 2609.25217

Limitations of quantum tomography in Higgs-boson decays to four leptons

Morgan Del Gratta·Fabio Maltoni·Davide Pagani·Giovanni Pelliccioli
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Abstract

We investigate the limitations of the two-qutrit quantum tomography in Higgs-boson decays to four charged leptons. At next-to-leading order, the standard reconstruction can yield an operator that is not positive semidefinite, even when radiatively improved spin-analysing powers are used. We trace this failure to the coherent combination of photon- and Z-mediated contributions to the off-shell dilepton system, whose distinct production and decay structures invalidate the assumed universal decay analysers. Nevertheless, the rank-two angular sector remains accessible and perturbatively stable, enabling a robust lower bound on the squared concurrence, and hence a reliable assessment of entanglement beyond leading order.

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Morgan Del Gratta, Fabio Maltoni, Davide Pagani, Giovanni Pelliccioli. 2026-09-21. Limitations of quantum tomography in Higgs-boson decays to four leptons. https://arxiv.org/abs/2609.25217

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