Spin Polarization Formula for Dirac Fermions at Local Equilibrium

Understand

We derive a Cooper-Frye type spin polarization formula for Dirac fermions at local thermal equilibrium described by a grand canonical ensemble specified by temperature, fluid velocity, chemical potential, and spin potential.

• We discuss the physical meaning of different contributions to spin polarization and compare them with previous works.
• The present formula provides machinery to convert the spin potential computed in, e.g., relativistic spin hydrodynamics to the spin polarization observable in, e.g., heavy-ion collisions.