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Excitation function for global Λ polarization in relativistic heavy-ion collisions with the core-corona model

Alejandro Ayala1, José Jorge Medina-Serna1,*, Isabel Domínguez2, and María Elena Tejeda-Yeomans3

  • 1Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Apartado Postal 70-543, CdMx 04510, Mexico
  • 2Departamento de Física, Facultad de Ciencias Naturales y Exactas, Universidad Autónoma de Sinaloa, Avenida de las Américas y Boulevard Universitarios, Ciudad Universitaria, Culiacán, 80000, Mexico
  • 3Facultad de Ciencias-CUICBAS, Universidad de Colima, Bernal Díaz del Castillo No. 340, Colonia Villas San Sebastián, Colima, 28045, Mexico

  • *Contact author: jose.medina@correo.nucleares.unam.mx
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Phys. Rev. D 114, 016034 – Published 31 July, 2026

DOI: https://doi.org/10.1103/fbt2-9gn1

Abstract

We compute the excitation function of the global Λ polarization in semicentral heavy-ion collisions within a core-corona framework, where the interaction region is described as a dense core and a dilute corona separated by a critical value of the participant density. An important ingredient in the model is the intrinsic polarization functions in each of the two regions. These are computed from a field-theoretical approach where the vortical motion of the medium is included in an effective fermion propagator, which we derive explicitly. The interactions in the core and the corona are transmitted by suitable mediators at finite temperature and baryon chemical potential; gluons for the former and σ-mesons for the latter. The temperatures and baryon chemical potentials are related to the collision energies along the chemical freezeout curve. By allowing the cross section for Λ production in the nuclear environment to take on values below the nucleon–nucleon threshold cross section, the calculation describes the lowest energy polarization data point. For the centralities corresponding to the experimental data, we find that the contribution from the corona is the dominant one and that a lifetime, and correspondingly a volume of this region which becomes larger for the smaller energies due to stopping, is an essential ingredient in the calculation. Overall, the model provides a good description of the excitation function across the full experimental range and predicts a robust maximum near sNN∼3  GeV that remains stable under reasonable variations of the freezeout curve and the proton–proton Λ production threshold to account for subthreshold production in a nuclear environment.

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Phys. Rev. D 114, 016034– Published 31 July, 2026
  • Received 14 April 2026
  • Accepted 17 June 2026
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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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