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  • Open Access

Freeze-out at constant energy density and spin polarization in heavy-ion collisions

Andrea Palermo

Masoud Shokri

  • Center for Nuclear Theory, Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794–3800, USA

  • Institut für Theoretische Physik, Johann Wolfgang Goethe–Universität, Max-von-Laue-Straße 1, D–60438 Frankfurt am Main, Germany

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Phys. Rev. D 112, 076011 – Published 10 October, 2025

DOI: https://doi.org/10.1103/2qsx-kgwr

Abstract

Using the local equilibrium density operator, we develop a geometry-informed linear response theory that takes into account the parametrization of the freeze-out hypersurface before the gradient expansion is carried out. Assuming local equilibrium on an iso-energy density hypersurface, we study the Λ hyperon spin polarization, and compute corrections to the isothermal case due to finite density. We argue that corrections to isothermal freeze-out should be small, and that even in heavy ion collisions with energy as low as sNN=11.5  GeV they constitute at most a 10% effect. They may, however, become relevant for local polarization observables.

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Phys. Rev. D 112, 076011– Published 10 October, 2025
  • Received 1 August 2025
  • Accepted 11 September 2025
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