Polarization of vector mesons in non-equilibrium hydrodynamics with spin

Abstract:

One of the most interesting developments in the investigation of quark-

gluon plasma was the discovery that the vorticose fluid created in heavy

ion collisions polarizes Lambda baryons and aligns spin of quarkonia

(bound quark-antiquark states) and vector mesons [1]. This opened a

new deep field of investigation, since the interaction of spin and vor-

ticity in systems close to local equilibrium is not understood even on

a conceptual level. Here, we argue that spin alignment of hadrons of

spin 1 and higher provide a unique window into the study of hydro-

dynamics with spin, because it is capable to probe non-equilibrium

between spin density and vorticity. This happens because most of the

full 3X3 density matrix is in principle accessible experimentally, and

non-zero off-diagonal matrix elements can be directly linked to such

non-equilibrium. We illustrate this using a coalescence model for light

vector mesons [2] as well as a potential model for quarkonia, and com-

pare our calculations to experimental data [3].