Speaker
Description
We investigate the rotational Brownian motion of heavy quarks in the QCD medium as a framework to study spin polarization of open heavy-flavor hadrons in relativistic heavy-ion collisions. We derive analytical expressions for vector and tensor polarization, corresponding to baryon spin polarization and vector meson spin alignment, respectively. Heavy quarks, produced in early hard scatterings, acquire spin polarization from the intense transient electromagnetic fields generated in off-central collisions, and subsequently undergo path-length dependent depolarization as they traverse the anisotropic quark-gluon plasma. We demonstrate that the transverse momentum dependence of heavy quark polarization serves as a distinctive signature of the initial magnetic field, and present comparisons with recent ALICE data on $D^{*+}$ meson spin alignment along with predictions for open charm baryons. Furthermore, we introduce polarization harmonics of open heavy-flavor hadrons as a novel observable directly sensitive to the initial spatial eccentricities of the fireball geometry, thereby establishing heavy-flavor polarization anisotropies as a complementary probe of early-time collision dynamics. Quantitative estimates of the second polarization harmonic are presented in connection with the recently reported $D^{*+}$ spin alignment by the ALICE Collaboration.