Quantum Observables in Top Quark Physics and Their Sensitivity to CP Violation

par Dr Priyanka Lamba (Louvain U., CP3)

vendredi 13 nov. 2026, 14:00 → 16:00 Europe/Paris

LPCA

High-energy colliders produce elementary particles with spin whose final states can be described as multi-qubit, qudit, or hybrid quantum systems. The spin density matrix encodes the complete spin information of a scattering process and gives access to a rich hierarchy of quantum-information observables — entanglement, Bell inequality violation, quantum discord, and magic — that go well beyond conventional collider quantities such as rates, angular asymmetries, and spin correlations. Developing such quantum-sensitive probes is especially timely given the absence of direct new-physics signals.

This talk begins with an introduction to the hierarchy of quantum correlations, placing entanglement, Bell inequality violation, quantum discord, and magic within a unified framework, before discussing how these observables can be accessed at colliders via quantum tomography. Since spin polarization is not directly measured at colliders, the full spin density matrix must be reconstructed from decay angular distributions. Examples in two-qubit and two-qutrit systems illustrate how different observables probe complementary structures of the density matrix.

The central focus is CP violation in the $t\bar{t}$ system, used as a probe of new physics beyond the Standard Model — whose existence is independently required to explain the observed matter-antimatter asymmetry of the Universe. In the Fano–Bloch decomposition of the spin density matrix, CP-violating new-physics effects manifest in structures such as $(B - B')$ and the antisymmetric part of the spin-correlation matrix $C$. I show how a range of quantum observables — concurrence, quantum discord, trace distance, and magic, alongside conventional CP-odd asymmetries — exhibit different and complementary sensitivity to these new-physics operators. I present results for different production mechanisms relevant to various collider environments and discuss how the tomographic framework can systematically disentangle CP violation arising in production from that in decay.