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arXiv:2610.27404

Non-Classicality in $tW$ system via negativity and geometric quantum discord

Amir Subba, Yu Shi

hep-phquant-phSubmitted Oct 19, 2026• Announced Oct 21, 2026• 0 citations
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Abstract

We perform a phenomenological study of non-classical correlations in the mixed-dimensional qubit-qutrit system realized by leading order $pp\to tW$ production at $\sqrt{s}=13$ TeV in the leptonic final state. The two missing neutrinos are reconstructed with conditional normalizing flows trained on simulated detector-level objects, and the joint spin density matrix $ρ_{tW}\in\mathcal{H}_2\otimes\mathcal{H}_3$ is obtained in a generalized Bloch representation from the angular distributions of the leptonic decay products. Non-classical correlations are quantified using the Peres--Horodecki negativity and geometric quantum discord. We quantify the correlations at different region of $m_{tW}$ at the reconstruction level within the Standard Model and the impact of two reducible backgrounds viz. $t\bar{t}$ and $WWj$ processes, tagged using boosted decision trees. We further study the behavior of correlations in presence of anomalous chromomagnetic and chromoelectric dipole moments of the top quark. The sensitivity reach of the quantum observables along with polarization and spin correlation parameters are reported for current LHC and future HL-LHC scenario.

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Non-Classicality in tWtWtW system via negativity and geometric quantum discord
We perform a phenomenological study of non-classical correlations in the mixed-dimensional qubit-qutrit system realized by leading order pp→tWpp\to tWpp→tW production at s=13\sqrt{s}=13s​=13 TeV in the leptonic final state. The two missing neutrinos are reconstructed with conditional normalizing flows trained on simulated detector-level objects, and the joint spin density matrix ρtW∈H2⊗H3ρ_{tW}\in\mathcal{H}_2\otimes\mathcal{H}_3ρtW​∈H2​⊗H3​ is obtained in a generalized Bloch representation from the angular distributions of the leptonic decay products. Non-classical correlations are quantified using the Peres--Horodecki negativity and geometric quantum discord. We quantify the correlations at different region of mtWm_{tW}mtW​ at the reconstruction level within the Standard Model and the impact of two reducible backgrounds viz. ttˉt\bar{t}ttˉ and WWjWWjWWj processes, tagged using boosted decision trees. We further study the behavior of correlations in presence of anomalous chromomagnetic and chromoelectric dipole moments of the top quark. The sensitivity reach of the quantum observables along with polarization and spin correlation parameters are reported for current LHC and future HL-LHC scenario.
Top and anti-top quark pair production at LHC provides a unique setting to probe non-classical correlations at the TeV scale. We study quantum information (QI) properties of the ttˉt\bar{t}ttˉ spin state in pppppp collisions at s=13\sqrt{s}=13s​=13 TeV within the Standard Model Effective Field Theory (SMEFT), focusing on dimension-6 operators that induce anomalous chromo- and weak dipole moments of the top quark within their current experimental bounds. The ttˉt\bar{t}ttˉ spin density matrix is reconstructed from the joint angular distribution of the final state charged leptons in the kkk-rrr-nnn helicity basis. We analyze three complementary QI quantities: concurrence-based quantum entanglement (QE), geometric quantum discord (GQD), and the Bell parameter,across four ttˉt\bar{t}ttˉ invariant-mass bins. Within the Standard Model (SM), non-vanishing QE appears only near threshold (mttˉ≲400m_{t\bar{t}}\lesssim 400mttˉ​≲400 GeV), while GQD remains nonzero across the full phase space, indicating persistent non-classical correlations even for separable states. Anomalous chromo-dipole interactions modify these observables primarily near threshold: μ^t\hatμ_tμ^​t​ induces asymmetric shifts, whereas d^t\hat{d}_td^t​ produces a mild symmetric response without Bell inequality violation. Among weak dipole operators, the CP-even coupling C2VC_2^VC2V​ generates the largest deformation of the QI observables, while ΔC1A,VΔC_1^{A,V}ΔC1A,V​ leave them unchanged. These results demonstrate that QI observables derived from the ttˉt\bar{t}ttˉ spin density matrix provide a complementary probe of anomalous top-quark interactions with distinct sensitivity to CP-even and CP-odd operator structures.
Hyperon-antihyperon pairs produced from electron-positron annihilations provide a promising platform for exploring quantum-information properties in particle physics. In this work, we analyze quantum steering and quantum discord in hyperon-antihyperon systems produced from e + e − annihilations, based on the X -shaped spin density matrix reconstructed via quantum state tomography. We show that the behaviors of these correlations differ from those observed in elementary particle-antiparticle systems such as top quarks and τ leptons, owing to the polarization effects specific to hyperon decays. From the results, we examine the hierarchy of quantum correlations in hyperon-antihyperon systems, Bell nonlocality ⊂ steering ⊂ entanglement ⊂ discord . We also discuss the role of experimental loopholes and the impact of quantum decoherence in collider-based studies of quantum correlations.
The characterization of quantum discord (QD) has been well understood only for two-qubit states and is little known for mixed states beyond qubits. In this work, thermal quantum discord is studied for a qutrit system in different magnetic fields, where classical correlation and entanglement negativity are calculated for comparison. It is shown that the discord is more robust against temperature than the negativity. For a suitable region of magnetic field and its direction, the discord is non-zero while the negativity is zero. When the system is at a lower temperature, these three quantities, however, display a similar behavior for the varied field and direction, and their discontinuities come from crossovers between different ground states in the system. Moreover, the inequality between the quantum and classical correlations depends upon the system parameters as well as the temperature. In particular, both correlations are equal at a suitable field, direction, and temperature. Remarkably, such an equality remains for a strong field in the antiparallel direction, while both correlations in two-qubit systems are identical for any antiparallel field and temperature. These are useful for quantum information and understanding quantum correlations in qutrit mixed states.
A bstract There has been an increasing interest in exploring quantities associated with quantum information at colliders. We perform a detailed analysis describing how to measure the quantum discord in the top anti-top quantum state at the Large Hadron Collider (LHC). While for pure states, quantum discord, entanglement, and Bell nonlocality all probe the same correlations, for mixed states they probe different aspects of quantum correlations. The quantum discord, in particular, is interesting because it aims to encapsulate all correlations between systems that cannot have a classical origin. We employ two complementary approaches for the study of the top anti-top system, namely the decay method and the kinematic method. We highlight subtleties associated with measuring discord for reconstructed quantum states at colliders. Usually quantum discord is difficult to compute due to an extremization that must be performed. We show, however, that for the tt‾ t\overline{t} tt t t ¯ system this extremization can be performed analytically and we provide closed-form formulas for the quantum discord. We demonstrate that with current LHC datasets, quantum discord can be observed at 3 . 6 – 5 . 7 σ , depending on the signal region, with the decay method and can be measured at a precision of 0 . 1 – 0 . 2% with the kinematic method. At the high luminosity LHC, the observation of quantum discord is expected to be > 5 σ using both the decay and kinematic methods and can be measured with a precision of 5% with the decay method and 0 . 05% with the kinematic method. Additionally, we identify the kinematic cuts at the LHC to isolate the tt‾ t\overline{t} tt t t ¯ state that is separable but has non-zero discord. By systematically investigating quantum discord for the first time through a detailed collider analysis, this work expands the toolkit for quantum information studies in particle physics and lays the groundwork for deeper insights into the quantum properties in high-energy collisions.
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