Probing Nature's Strongest Magnetic Field Using Charm Quarks in Ultra-Relativistic Heavy-Ion Collisions

Objectif

In non-central heavy-ion collisions, the geometry and motion of the colliding nuclei are theorized to produce the strongest magnetic fields known in nature—reaching magnitudes of ~10¹⁹ Gauss—alongside large angular momentum. However, the existence, lifetime, and influence of these ultra-strong magnetic fields remain unverified experimentally due to the lack of direct, sensitive probes. This project proposes a novel, two-pronged experimental approach to address this gap. The polarization of Λc⁺ baryons will be measured, providing access to charm quark spin alignment, which is sensitive to early-time magnetic fields due to the prompt production of heavy quarks. A polarization difference between Λc⁺ and Λc⁻ would offer a direct measure of the magnetic field's magnitude. Simultaneously, the directed flow (v₁) of D mesons will be analyzed, where a charge-dependent v₁ asymmetry can disentangle the influence of the magnetic field from that of the tilted initial geometry. Together, these complementary observables will estimate the strongest magnetic field in nature and constrain the electrical conductivity of the QGP. Using high-precision Run 3 ALICE data, the project aims to perform the first integrated study of these phenomena, contributing to a deeper understanding of strong interactions under extreme conditions and establishing new intradisciplinary links with cosmology, astrophysics, and condensed matter systems.