  Quarks produced in the early stage of non-central heavy-ion collisions could
develop a global spin polarization along the opposite direction of the reaction
plane due to the spin-orbital coupling via parton interaction in a medium that
has finite longitudinal flow shear along the direction of the impact parameter.
We study how such polarization evolves via multiple scattering in a viscous
quark-gluon plasma with an initial laminar flow. The final polarization is
found to be sensitive to the viscosity and the initial shear of local
longitudinal flow.
