Global quark polarization in non-central $A+A$ collisions

Understand

Partons produced in the early stage of non-central heavy-ion collisions can develop a longitudinal fluid shear because of unequal local number densities of participant target and projectile nucleons.

• Under such fluid shear, local parton pairs with non-vanishing impact parameter have finite local relative orbital angular momentum along the direction opposite to the reaction plane.
• Such finite relative orbital angular momentum among locally interacting quark pairs can lead to global quark polarization along the same direction due to spin-orbital coupling.
• Local longitudinal fluid shear is estimated within both Landau fireball and Bjorken scaling model of initial parton production.