Global angular momentum generation in heavy-ion reactions within a hadronic transport approach

Abstract

In 2017, the STAR collaboration at the Relativistic Heavy Ion Collider (RHIC) has measured finite global angular momentum in heavy-ion collisions through a spin polarization measurement of $\Lambda$ hyperons. This measurement revealed a high angular momentum of the heavy ions and provided experimental evidence for vorticity in the quark-gluon plasma (QGP) 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 non-equilibrium 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 \textit{et al} 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 $b=4-6$ fm for all beam energies from $\sqrt{s_{\mathrm{NN}}}=2.41-200$ 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.

arXiv comment8 pages, 6 figures

References in corpus (26)

• PYTHIA 6.4 Physics and Manual
• PYTHIA 6.2 Physics and Manual
• A Brief Introduction to PYTHIA 8.1
• Microscopic Models for Ultrarelativistic Heavy Ion Collisions
• Relativistic Hadron-Hadron Collisions in the Ultra-Relativistic Quantum Molecular Dynamics Model (UrQMD)
• Global $\Lambda$ hyperon polarization in nuclear collisions: evidence for the most vortical fluid
• Heavy Ion Collisions: The Big Picture, and the Big Questions
• Globally Polarized Quark-gluon Plasma in Non-central A+A Collisions
• Transport-theoretical Description of Nuclear Reactions
• Angular momentum conservation in heavy ion collisions at very high energy
• Study of relativistic nuclear collisions at AGS energies from p+Be to Au+Au with hadronic cascade model
• Particle production and equilibrium properties within a new hadron transport approach for heavy-ion collisions
• Rotating quark-gluon plasma in relativistic heavy ion collisions
• Study of Lambda polarization in relativistic nuclear collisions at sqrt{s}_NN = 7.7-200 GeV
• Relativistic Transport Approach for Nucleus-Nucleus Collisions from SIS to SPS Energies
• Polarization probes of vorticity in heavy ion collisions
• Vorticity in Heavy-Ion Collisions
• A study of vorticity formation in high energy nuclear collisions
• Global quark polarization in non-central $A+A$ collisions
• Polarization and Vorticity in the Quark Gluon Plasma
• Particle Production via Strings and Baryon Stopping within a Hadronic Transport Approach
• Measurement of global polarization of Λ hyperons in few-GeV heavy-ion collisions
• The effect of finite-range interactions in classical transport theory
• Frame Dependence of Parton Cascade Results
• Vorticity in the QGP liquid and $\Lambda$ polarization at the RHIC Beam Energy Scan
• Particle Production in AgAg Collisions at $E_{\mathrm{Kin}}=1.58A$ GeV within a Hadronic Transport Approach

Cited by in corpus (1)

• The Static Heavy Quark-Antiquark Potential within String Theory in Arbitrary Stationary Backgrounds