The observation of hyperon spin polarization in relativistic heavy-ion collisions provides a unique opportunity for studying local vorticity structures and inhomogeneities hydrodynamic fields in the quark-gluon plasma. However, a fundamental challenge persists: significant discrepancies between theory and experiment in local spin polarization measurements, the ``spin sign puzzle'', suggest an incomplete theoretical understanding. A key limitation of existing models based on quantum statistical theory at local equilibrium is their reliance on oversimplified geometries for the decoupling hypersurface. We propose a novel approach for dealing with the hypersurface with arbitrary geometry, which allows us to systematically derive corrections from gradients of the hydrodynamic fields and the local geometry. The new results naturally exclude unphysical contributions from gradients in the normal direction of the hypersurface, which provides a first-principle justification for the empirically imposed ``isothermal condition'' used in previous works. Beyond the immediate application to spin-1/2 fermions, our framework is readily generalized to particles with any spin and is therefore important for studying spin phenomena in relativistic heavy-ion collisions. A brief overview of recent experimental observations will also be presented.
Biography:
Xin-Li Sheng is a postdoc at University of Florence. He received his Ph.D. degree in physics from University of Science and Technology of China in 2020. During his Ph.D. training, he visited Goethe University in Germany as a cotutelle student and received a joint Ph.D. degree from Goethe University. From 2020 to 2022, he worked at Central China Normal University as a postdoctoral researcher. Xin-Li Sheng's research interests focus on spin-related theories, including quantum kinetics, statistical models, and spin hydrodynamics.
Prof. Huichao Song