Local polarization and isothermal local equilibrium in relativistic heavy ion collisions

TL;DR

This paper demonstrates that incorporating a new term in the spin polarization vector and assuming constant temperature in hydrodynamic models aligns predictions with experimental polarization data in relativistic heavy ion collisions, highlighting temperature sensitivity.

Contribution

It introduces a new term in the spin polarization vector and shows how assuming constant temperature improves model-data agreement in heavy ion collision polarization measurements.

Findings

Good fit to data at around 155 MeV temperature.

Longitudinal polarization component is highly temperature-sensitive.

Inclusion of the new term restores quantitative agreement.

Abstract

We show that the inclusion of a recently found additional term of the spin polarization vector at local equilibrium which is linear in the symmetrized gradients of the velocity field, and the assumption of hadron production at constant temperature restore the quantitative agreement between hydrodynamic model predictions and local polarization measurements in relativistic heavy ion collisions at $\sqrt{s_{\rm NN}} = 200$ GeV. The longitudinal component of the spin polarization vector turns out to be very sensitive to the temperature value, with a good fit around 155 MeV. The implications of this finding are discussed.