Holography of Low-Centrality Heavy Ion Collisions

TL;DR

This paper uses a holographic model to predict how hyperon polarizations in heavy ion collisions vary with centrality and impact energy, especially at smaller centralities and lower energies, providing testable predictions for future experiments.

Contribution

It introduces a holographic approach to predict hyperon polarization behavior at small centralities and lower impact energies, extending previous experimental observations.

Findings

Polarizations decrease then sharply increase at smaller centralities.

Predicted effects are most prominent at impact energy 27 GeV.

Model suggests observable polarization patterns below 200 GeV impact energy.

Abstract

Large vorticities in the Quark-Gluon Plasma produced in peripheral collisions studied by the STAR collaboration at the RHIC facility have been deduced from observations of polarizations of $\Lambda$ and $\overline{\Lambda}$ hyperons. Recently, the STAR collaboration has reported on the dependence of these polarizations on centrality, at impact energy 200 GeV and relatively large centralities $\mathcal{C} \geq 20\%$. The polarizations increase slowly with centrality, up to perhaps $\mathcal{C} = \,60 - 70\%$. Here we use a holographic model of the vortical QGP to make predictions regarding these polarizations for smaller centralities, ranging from $5 - 20\%$. The model predicts that as one moves downwards from $20\%$, $\Lambda/\overline{\Lambda}$ polarizations at first decrease but then \emph{increase} sharply, in a characteristic pattern which should be readily detected if collisions can be studied at impact energies below 200 GeV and centrality as low as $5 - 10\%$. The effect should be most evident at moderate impact energies below 200 GeV, so we give predictions for impact energy 27 GeV.