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Meson spin alignment and baryon polarization from coalescence with spin-vorticity nonequilibrium

Kayman J. Gonçalves1, Giorgio Torrieri1, and Radoslaw Ryblewski2

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Phys. Rev. C 112, 014901 – Published 7 July, 2025

DOI: https://doi.org/10.1103/gsv6-zydk

Abstract

We estimate both the polarization of spin 1/2 baryons and the spin density matrix coefficients of spin 1 mesons using a thermal model that incorporates vorticity and polarization to describe quarks, along with a coalescence formalism where spin and vorticity are not in equilibrium. We find that while our model is not predictive due to its considerable number of free parameters, it has the potential to explain several seemingly puzzling features of experimental spin measurements, such as the absence of baryon polarization alongside significant vector meson spin alignment. We suggest measuring meson spin off-diagonal matrix elements, and examining the dependence of polarization observables on azimuthal angles, as methods to falsify this model and gain insights into the freeze-out details of baryon and meson spin structure.

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Phys. Rev. C 112, 014901– Published 7 July, 2025
  • Received 24 October 2024
  • Revised 24 April 2025
  • Accepted 25 June 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.

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