Speaker
Description
In relativistic heavy ion collisions (HIC), strong vorticity can be generated for the produced quark gluon plasmas, which could lead to spin polarization of quarks and gluons inherited by the spin polarization of Lambda hyperons measured by the weak decay. Nevertheless, to understand the local distribution of vortical fields, the local spin polarization along the beam direction with the azimuthal angle dependence was further measured. It is however found that there exist various contributions from other sources such as the shear strength or chemical-potential gradients for local spin polarization on top of the vortical effect. In order to probe the local structure of vortical fields and obtain a baseline for additional corrections in and out of equilibrium on top of the vorticity, we investigate the hydrodynamic helicity polarization of Lambda hyperons, defined as the projection of the spin polarization vector along the directions of particle momenta, at RHIC-beam-energy-scan (BES) energies by utilizing the relativistic (3+1) dimensional viscous hydrodynamics framework with prescribed initial conditions. As opposed to local spin polarization at high energy collisions, our hydrodynamic simulations demonstrate that the helicity polarization induced by the kinetic vorticity dominates over other contributions at intermediate and low collision energies. Our findings hence provide an opportunity to probe the fine structure of local kinetic vorticity as a function of azimuthal angle at intermediate and low collision energies by mapping our predictions to the future measurements in experiments.
