Quantum properties of heavy-fermion pairs at a lepton collider with polarised beams

• URL: http://arxiv.org/abs/2601.09558v1
• Date: Wed, 14 Jan 2026 15:28:49 GMT
• Title: Quantum properties of heavy-fermion pairs at a lepton collider with polarised beams
• Authors: Mohammad Mahdi Altakach, Priyanka Lamba, Fabio Maltoni, Kazuki Sakurai,
• Abstract summary: We investigate the quantum properties of heavy-fermion pairs, such as $tbar t$ or $+-$, produced in lepton-lepton collisions with polarised beams.<n> Focusing on spin correlations, entanglement, Bell-inequality violation, and quantum-information--theoretic measures such as purity and magic, we analyse how beam polarisation shapes the structure of the spin-density matrix.
• Score: 0.0
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: We investigate the quantum properties of heavy-fermion pairs, such as $t\bar t$ or $τ^+τ^-$, produced in lepton-lepton collisions with polarised beams. Focusing on spin correlations, entanglement, Bell-inequality violation, and quantum-information--theoretic measures such as purity and magic, we analyse how beam polarisation shapes the structure of the spin-density matrix. We derive analytic expressions for a wide range of helicity configurations, including both Standard Model contributions and generic new-physics effects parametrised by scalar, vector, and tensor four-fermion operators within an effective field theory framework. We show that beam polarisation unlocks a substantially richer set of spin configurations and significantly enhances sensitivity to non-standard interactions. As a phenomenological application, we study $t\bar t$ production at a future linear collider and demonstrate that quantum observables provide a comprehensive and complementary probe of top-quark interactions and stronger constraints on the scale of new physics.

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