Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2410.10980

Constraining New Physics with $h\rightarrow VV$ Tomography

Matthew Sullivan

Published Oct 14, 2024• 0 citations
arXivHTMLPDF

Abstract

The application of quantum information methods to high energy physics has recently been gaining traction. In particular, reconstructing density matrices and measuring entanglement have been investigated for top quark decays and Higgs decays. This paper will further investigate the utility of density matrices for Higgs decays to vector bosons. Imprints of new physics, whether CP-even or CP-odd, in $h \rightarrow VV$ will generally change the spin density matrix, and so the tomographic reconstruction of the density matrix can constrain, or potentially detect, such new physics. New physics, expressed in the language of the Standard Model effective field theory, is analyzed in this framework of quantum tomography. Prospects for $h \rightarrow WW$ are good due to the fully chiral coupling of the $W$ boson to fermions, while $h \rightarrow ZZ$ requires around an order of magnitude more events to reach comparable sensitivity.

DOI
10.48550/arxiv.2410.10980

Related papers

Odd Physics Off the Diagonal: Constraining CP-violating SMEFT with Quantum Tomography

Avalon Roberts, Patrick Dougan, Alexander Oh +1 more

New sources of charge-parity (CP) violation beyond those described in the Standard Model (SM) are required to explain the observed matter--antimatter asymmetry of the Universe. The Standard Model Effective Field Theory (SMEFT) provides a framework to introduce additional electroweak sources of CP-odd physics in a model-independent manner. However, these CP-violating signatures are mostly degenerate to CP-even SMEFT operators in polarisation-blind observables, distinguishable only in the SM-New Physics (NP) interference using the azimuthal decay angle. Using Quantum Tomography techniques, we present a new approach to constraining these NP effects. Reconstructing the spin density matrix (SDM) of a diboson system, we go beyond `interference resurrection' to exploit the full signature of the Beyond-SM physics, including the pure quadratic NP terms. We show that this approach provides superior simultaneous sensitivity to characteristic features of CP-even and CP-odd contributions, including effects not fully captured by traditional angular observables.

hep-phCross-listedarXiv:2604.21857•Apr 24, 2026

Quantum Tomography and Entanglement in Semi-Leptonic $h\to VV^*$ Decays at Higher Orders

Dorival Gonçalves, Ajay Kaladharan, Alberto Navarro

Angular correlations in Higgs decays to electroweak gauge bosons, $h \to ZZ^*, WW^*$, provide a powerful probe of both new physics effects and quantum information observables. We present a systematic study of semi-leptonic Higgs decays $h \to V V^* \to \ell^+\ell^- q\bar{q}$ and $\ell^\pm ν_\ell q\bar{q}'$, including finite final state fermion masses, NLO QCD, and NLO electroweak corrections. We show that finite final state quark masses can induce effects that go beyond the two-qutrit description in more inclusive regimes, while remaining controllable with suitable kinematic selections. QCD corrections lead to modest percent-level shifts, whereas electroweak corrections can significantly modify the angular structure, particularly in the $h\to ZZ^*$ channels. We assess the impact of these effects on the reconstructed density matrix and entanglement measures, finding that, although they modify the angular observables, the semi-leptonic channels are better approximated by a two-qutrit description than the fully leptonic decay $h\to e^+e^-μ^+μ^-$.

hep-phCross-listedarXiv:2604.16218•Apr 20, 2026

Trace distance between density matrices: A nifty tool in new-physics searches

M. Fabbrichesi, Matthew Low, Luca Marzola

Quantum information methods have been brought to bear on high-energy physics, including the study of entanglement and Bell nonlocality in collider experiments. Quantum information observables have also been employed to constrain possible new-physics effects. We improve on this point by introducing quantum information tools routinely used to compare quantum states: the trace distance and the fidelity. We find that the former outperforms other quantum information observables considered in the literature and, together with the cross section, yields the strongest bounds on possible departures from the Standard Model. The power of the proposed methodology is demonstrated with three examples of new-physics searches. The first concerns the chromomagnetic dipole moment of the top quark and yields the first bound computed by means of quantum tomography and actual experimental data. The other two examples use Monte Carlo simulations and set the projected limits on the anomalous couplings of the τ leptons at Belle and at a future collider—which is taken to be LEP3. For these new-physics searches, we also compare the sensitivity of the trace distance to those of other quantum information quantities like concurrence, magic, and the fidelity distance. In passing, we provide the first determinations of magic in collider data by analyzing the top-quark pair production at the LHC and the charmonium decays. The significance is well above the 5 σ level in both the cases.

arXiv:2501.03311•Physical review. D/Physical review. D.•Jun 19, 2025•8 citations

Quantum detection of CP violation in the $t\bar{t}$ system: tomography

Priyanka Lamba, Fabio Maltoni, Olimpia Miniati +1 more

We develop a quantum-tomographic framework for determining whether possible CP-odd effects in $t\bar t$ events originate in production, in decay, or in both. In the narrow-width approximation, the process $I\to t\bar t\to b\ell^+ν\,\bar b\ell^-\barν$ factorises into a production density matrix and top and antitop decay density matrices. We extend the standard tomography procedure to a general anomalous $Wtb$ vertex and derive the corresponding angular distributions. Polar-angle distributions retain their usual tomographic form, up to modifications of the spin-analysing powers, and can therefore be used to reconstruct the production density matrix and test its CP properties. By contrast, dedicated azimuthal observables involving the $b$--lepton decay planes contain characteristic sine modulations that provide linear probes of possible new CP-violating interactions in the decay vertex. Combining the two classes of observables gives a systematic strategy for separating sources of CP violation in production and in decay. We illustrate the resulting angular signatures for representative $t\bar t$ production scenarios at hadron and lepton colliders.

hep-phCross-listedarXiv:2607.25034•Jul 29, 2026

Qubit-Qutrit Quantum Tomography of hadronic $Λφ$ and $ΛK^{\ast 0}$ systems

Veronica Kanachova, Feng Liu, Zhoudunming Tu

Quantum-information observables have emerged in recent years as new tools in nuclear and particle physics, from entanglement in top-quark pairs to spin correlations in $Λ\barΛ$ production. Extending these studies to unequal-spin hadronic final states poses a fundamental challenge: the $6\times6$ density matrix of a qubit-qutrit system contains 35 independent spin parameters, but the decays of $ΛV$ pairs, with $V=φ$ or $K^{*0}$, provide access to only 23 due to the hidden vector polarization from the strong decay. In this Letter, we formulate a qubit-qutrit quantum tomography (QQQT) technique for these spin-$\tfrac{1}{2}\otimes1$ systems and establish exact criteria for entanglement certification from the \textit{incomplete} density matrix. Compared with the $Λ\barΛ$ system, QQQT of $Λφ$ and $ΛK^{*0}$ provides a new probe of nonperturbative QCD hadronization, enabling a direct comparison of the spin evolution of entangled quark pairs produced from the vacuum as they hadronize into a baryon or a vector meson.

hep-phCross-listedarXiv:2609.11151•Sep 11, 2026

Quantum SMEFT tomography: top quark pair

Luca Mantani

In recent years, an interest in the study of quantum information has grown within the high-energy particle physics community. The possibility to establish the presence of entanglement at particle colliders, such as the Large Hadron Collider (LHC) at CERN, is a novel and thrilling research direction, offering the opportunity to push quantum mechanics to its limits by using the heaviest fundamental particle: the top quark. With this in mind, we propose to use measurements of quantum entanglement to probe the behaviour of fundamental interactions and to search for New Physics at high energy within the Standard Model Effective Field Theory paradigm. Inspired by recent proposals to measure entanglement of top quark pairs produced at the LHC, we examine how the existence of new interactions between fundamental particles modify the Standard Model expectations. By performing analytical calculations, we unveil a non-trivial pattern of effects depending on the kinematical phase space configurations.

arXiv:2211.03428•International Conference on High Energy Physics (ICHEP)•Nov 8, 2022•1 citation
Constraining New Physics with h→VVh\rightarrow VVh→VV Tomography
The application of quantum information methods to high energy physics has recently been gaining traction. In particular, reconstructing density matrices and measuring entanglement have been investigated for top quark decays and Higgs decays. This paper will further investigate the utility of density matrices for Higgs decays to vector bosons. Imprints of new physics, whether CP-even or CP-odd, in h→VVh \rightarrow VVh→VV will generally change the spin density matrix, and so the tomographic reconstruction of the density matrix can constrain, or potentially detect, such new physics. New physics, expressed in the language of the Standard Model effective field theory, is analyzed in this framework of quantum tomography. Prospects for h→WWh \rightarrow WWh→WW are good due to the fully chiral coupling of the WWW boson to fermions, while h→ZZh \rightarrow ZZh→ZZ requires around an order of magnitude more events to reach comparable sensitivity.
New sources of charge-parity (CP) violation beyond those described in the Standard Model (SM) are required to explain the observed matter--antimatter asymmetry of the Universe. The Standard Model Effective Field Theory (SMEFT) provides a framework to introduce additional electroweak sources of CP-odd physics in a model-independent manner. However, these CP-violating signatures are mostly degenerate to CP-even SMEFT operators in polarisation-blind observables, distinguishable only in the SM-New Physics (NP) interference using the azimuthal decay angle. Using Quantum Tomography techniques, we present a new approach to constraining these NP effects. Reconstructing the spin density matrix (SDM) of a diboson system, we go beyond `interference resurrection' to exploit the full signature of the Beyond-SM physics, including the pure quadratic NP terms. We show that this approach provides superior simultaneous sensitivity to characteristic features of CP-even and CP-odd contributions, including effects not fully captured by traditional angular observables.
Quantum Tomography and Entanglement in Semi-Leptonic h→VV∗h\to VV^*h→VV∗ Decays at Higher Orders
Angular correlations in Higgs decays to electroweak gauge bosons, h→ZZ∗,WW∗h \to ZZ^*, WW^*h→ZZ∗,WW∗, provide a powerful probe of both new physics effects and quantum information observables. We present a systematic study of semi-leptonic Higgs decays h→VV∗→ℓ+ℓ−qqˉh \to V V^* \to \ell^+\ell^- q\bar{q}h→VV∗→ℓ+ℓ−qqˉ​ and ℓ±νℓqqˉ′\ell^\pm ν_\ell q\bar{q}'ℓ±νℓ​qqˉ​′, including finite final state fermion masses, NLO QCD, and NLO electroweak corrections. We show that finite final state quark masses can induce effects that go beyond the two-qutrit description in more inclusive regimes, while remaining controllable with suitable kinematic selections. QCD corrections lead to modest percent-level shifts, whereas electroweak corrections can significantly modify the angular structure, particularly in the h→ZZ∗h\to ZZ^*h→ZZ∗ channels. We assess the impact of these effects on the reconstructed density matrix and entanglement measures, finding that, although they modify the angular observables, the semi-leptonic channels are better approximated by a two-qutrit description than the fully leptonic decay h→e+e−μ+μ−h\to e^+e^-μ^+μ^-h→e+e−μ+μ−.
Quantum information methods have been brought to bear on high-energy physics, including the study of entanglement and Bell nonlocality in collider experiments. Quantum information observables have also been employed to constrain possible new-physics effects. We improve on this point by introducing quantum information tools routinely used to compare quantum states: the trace distance and the fidelity. We find that the former outperforms other quantum information observables considered in the literature and, together with the cross section, yields the strongest bounds on possible departures from the Standard Model. The power of the proposed methodology is demonstrated with three examples of new-physics searches. The first concerns the chromomagnetic dipole moment of the top quark and yields the first bound computed by means of quantum tomography and actual experimental data. The other two examples use Monte Carlo simulations and set the projected limits on the anomalous couplings of the τ leptons at Belle and at a future collider—which is taken to be LEP3. For these new-physics searches, we also compare the sensitivity of the trace distance to those of other quantum information quantities like concurrence, magic, and the fidelity distance. In passing, we provide the first determinations of magic in collider data by analyzing the top-quark pair production at the LHC and the charmonium decays. The significance is well above the 5 σ level in both the cases.
Quantum detection of CP violation in the ttˉt\bar{t}ttˉ system: tomography
We develop a quantum-tomographic framework for determining whether possible CP-odd effects in ttˉt\bar tttˉ events originate in production, in decay, or in both. In the narrow-width approximation, the process I→ttˉ→bℓ+ν bˉℓ−νˉI\to t\bar t\to b\ell^+ν\,\bar b\ell^-\barνI→ttˉ→bℓ+νbˉℓ−νˉ factorises into a production density matrix and top and antitop decay density matrices. We extend the standard tomography procedure to a general anomalous WtbWtbWtb vertex and derive the corresponding angular distributions. Polar-angle distributions retain their usual tomographic form, up to modifications of the spin-analysing powers, and can therefore be used to reconstruct the production density matrix and test its CP properties. By contrast, dedicated azimuthal observables involving the bbb--lepton decay planes contain characteristic sine modulations that provide linear probes of possible new CP-violating interactions in the decay vertex. Combining the two classes of observables gives a systematic strategy for separating sources of CP violation in production and in decay. We illustrate the resulting angular signatures for representative ttˉt\bar tttˉ production scenarios at hadron and lepton colliders.
Qubit-Qutrit Quantum Tomography of hadronic ΛφΛφΛφ and ΛK∗0ΛK^{\ast 0}ΛK∗0 systems
Quantum-information observables have emerged in recent years as new tools in nuclear and particle physics, from entanglement in top-quark pairs to spin correlations in ΛΛˉΛ\barΛΛΛˉ production. Extending these studies to unequal-spin hadronic final states poses a fundamental challenge: the 6×66\times66×6 density matrix of a qubit-qutrit system contains 35 independent spin parameters, but the decays of ΛVΛVΛV pairs, with V=φV=φV=φ or K∗0K^{*0}K∗0, provide access to only 23 due to the hidden vector polarization from the strong decay. In this Letter, we formulate a qubit-qutrit quantum tomography (QQQT) technique for these spin-12⊗1\tfrac{1}{2}\otimes121​⊗1 systems and establish exact criteria for entanglement certification from the \textit{incomplete} density matrix. Compared with the ΛΛˉΛ\barΛΛΛˉ system, QQQT of ΛφΛφΛφ and ΛK∗0ΛK^{*0}ΛK∗0 provides a new probe of nonperturbative QCD hadronization, enabling a direct comparison of the spin evolution of entangled quark pairs produced from the vacuum as they hadronize into a baryon or a vector meson.
In recent years, an interest in the study of quantum information has grown within the high-energy particle physics community. The possibility to establish the presence of entanglement at particle colliders, such as the Large Hadron Collider (LHC) at CERN, is a novel and thrilling research direction, offering the opportunity to push quantum mechanics to its limits by using the heaviest fundamental particle: the top quark. With this in mind, we propose to use measurements of quantum entanglement to probe the behaviour of fundamental interactions and to search for New Physics at high energy within the Standard Model Effective Field Theory paradigm. Inspired by recent proposals to measure entanglement of top quark pairs produced at the LHC, we examine how the existence of new interactions between fundamental particles modify the Standard Model expectations. By performing analytical calculations, we unveil a non-trivial pattern of effects depending on the kinematical phase space configurations.