Speaker
Description
Quantum-information observables offer new tools for probing collider events beyond traditional quantities such as cross sections and invariant masses. This work investigates quantum entanglement in top–antitop pairs produced via e⁺e⁻ → tt̄, using spin density matrices generated with the recently developed Density Mode framework within MadGraph5_aMC@NLO. Events were simulated at leading order for nine center-of-mass energies between 350 GeV and 3 TeV using unpolarized beams. A custom Python pipeline was deployed to reconstruct the spin density matrices and evaluate Purity, Concurrence, Entanglement of Formation, and Negativity as functions of the top quark production angle.
The angular peak position of the entanglement observables stabilizes above ~1–1.5 TeV, settling near cos θ ≈ −0.51, in agreement with theoretical predictions once a sign-convention correction is applied to the angle definition. By contrast, the peak magnitude of these observables continues to increase up to 3 TeV, asymptotically approaching but not yet reaching the maximal mathematical bounds, consistent with residual m_t²/s corrections at the highest energy studied. Bootstrap resampling (200 iterations) confirms that this qualitative behavior is statistically robust. These results provide a systematic, unpolarized baseline for the energy evolution of quantum-information observables in the top sector, serving as a precise Standard Model reference for future high-energy e⁺e⁻ collider programs and complementing recent LHC threshold measurements.
