Speaker
Description
The quark constituents of the fireball created in relativistic heavy-ion
collisions carry intrinsic spin. Whether these spin degrees of freedom fully
thermalize remains an open question. Insights from kinetic theory suggest that spin
relaxes on a longer timescale compared to momentum. Polarization observables in
experiments offer valuable probes into this issue. While the assumption of local
equilibrium for spin degrees of freedom at freeze-out successfully reproduces
global polarization data, it fails to capture the correct sign of longitudinal
polarization without invoking the isothermal approximation-indicating the presence
of nontrivial spin dynamics. Until recently, no tool has been available to study such
dynamics in detail. In this work [1], we numerically solve (3+1)-dimensional
dissipative spin hydrodynamics on top of a realistic hydrodynamic background. We
investigate the time evolution of the spin potential under three different interaction
scenarios for the QGP fireball produced in Au+Au collisions at top RHIC energy.
Our results suggest that spin degrees of freedom may thermalize within the lifetime
of the fireball. We further apply our framework to describe the spin polarization of Λ
hyperons. The results indicate that dissipative effects play a critical role in correctly
reproducing the sign of longitudinal polarization. [1] Sapna, S. K. Singh and D.
Wagner, arXiv:2503.22552
