Quantum tomography of diboson spin density matrices yields superior sensitivity to CP-even and CP-odd SMEFT contributions, including quadratic new-physics terms not captured by traditional angular observables.
Entanglement and Bell Nonlocality in $\tau^+ \tau^-$ at the LHC using Machine Learning for Neutrino Reconstruction
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abstract
Experiments at the CERN Large Hadron Collider (LHC) have accumulated an unprecedented amount of data corresponding to a large variety of quantum states. Although searching for new particles beyond the Standard Model of particle physics remains a high priority for the LHC program, precision measurements of the physical processes predicted in the Standard Model continue to lead us to a deeper understanding of nature at high energies. We carry out detailed simulations for the process $pp \to \tau^+\tau^- X$ to perform quantum tomography and to measure the quantum entanglement and the Bell nonlocality of the $\tau^+\tau^-$ two qubit state, including both statistical and systematic uncertainties. By using advanced machine learning techniques for neutrino momentum reconstruction, we achieve precise measurements of the full spin density matrix, a critical advantage over previous studies limited by reconstruction challenges for missing momenta. Our analysis reveals a clear observation of Bell nonlocality with high statistical significance, surpassing 5$\sigma$, establishing $\tau^+ \tau^-$ as an ideal system for quantum information studies in high-energy collisions. Given its experimental feasibility and the high expected sensitivity for Bell nonlocality, we propose that $\tau^+ \tau^-$ should be regarded as the new benchmark system for quantum information studies at the LHC, complementing and extending the insights gained from the $t\bar{t}$ system.
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representative citing papers
An automated framework in MadGraph5_aMC@NLO computes tree-level production spin-density matrices and quantum observables for generic collider processes, with validation on ttbar and VV and new applications to multi-top final states.
Transverse polarization in e+e- collisions generates maximally entangled fermion pairs in QED processes and boosts entanglement in electroweak and Bhabha scattering.
Under mild assumptions, local hidden variable theories become testable at colliders and can be disproved via Bell-like inequalities for muon and tau pairs.
Including soft gluons in Monte Carlo generators for DIS aligns parton distributions with inclusive PDFs and makes entropy grow with decreasing x, indicating initial-state origin of the bulk entropy.
citing papers explorer
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Odd Physics Off the Diagonal: Constraining CP-violating SMEFT with Quantum Tomography
Quantum tomography of diboson spin density matrices yields superior sensitivity to CP-even and CP-odd SMEFT contributions, including quadratic new-physics terms not captured by traditional angular observables.
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Automated computation of spin-density matrices and quantum observables for collider physics
An automated framework in MadGraph5_aMC@NLO computes tree-level production spin-density matrices and quantum observables for generic collider processes, with validation on ttbar and VV and new applications to multi-top final states.
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Spin Correlation and Quantum Entanglement of Fermion Pairs in Transversely Polarized $e^-e^+$ Collisions
Transverse polarization in e+e- collisions generates maximally entangled fermion pairs in QED processes and boosts entanglement in electroweak and Bhabha scattering.
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Understanding Bell locality tests at colliders
Under mild assumptions, local hidden variable theories become testable at colliders and can be disproved via Bell-like inequalities for muon and tau pairs.
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Entanglement entropy, Monte Carlo event generators, and soft gluons DIScovery
Including soft gluons in Monte Carlo generators for DIS aligns parton distributions with inclusive PDFs and makes entropy grow with decreasing x, indicating initial-state origin of the bulk entropy.
- Probing Quantum Entanglement in $\tau^+\tau^-$ Pairs via the $\pi\pi$ Channel at STCF