Scientific Papers

Phys. Rev. C 108, 044903 (2023)

In 2017, the STAR collaboration at the BNL Relativistic Heavy Ion Collider measured finite global angular momentum in heavy-ion collisions through a spin polarization measurement of Λ hyperons. This measurement revealed a high angular momentum of the heavy ions and provided experimental evidence for vorticity in the quark-gluon plasma for the first time. In order to investigate the underlying mechanisms, a dynamic description of the transfer of angular momentum is required. In this work, the microscopic nonequilibrium transport approach SMASH (simulating many accelerated strongly interacting hadrons) is applied to study the generation of global angular momentum by the interaction of two nuclei. As SMASH provides access to the whole phase-space evolution of every particle at any given time, it allows to assess the fraction of angular momentum generated in the fireball by all participants. We confirm the previous modeling by Becattini et al., [Phys. Rev. C 77, 024906 (2008)] within a geometric Glauber model approach, which found that the angular momentum transfer reaches a unique maximum in mid-central collisions during time evolution. The corresponding impact parameter is around b=46 fm for all beam energies from sNN=2.41200 GeV. Even though angular momentum is not conserved locally in the transport approach a priori, we identify the contributions to the conservation violation and propose optimal setups for different energy regimes that recover conservation, based upon the test particle method and the treatment of Fermi motion. Furthermore, the system size and centrality dependence are investigated.

  • Received 9 May 2023
  • Accepted 31 August 2023


©2023 American Physical Society

Nuclear Physics

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