Is Hyperon Polarization in Relativistic Heavy Ion Collisions Connected to Axial U(1) Symmetry Breaking at High Temperature?

Abstract

Experiments at the Relativistic Heavy Ion Collider (RHIC) have measured the net polarization of $\Lambda$ and $\bar{\Lambda }$ hyperons and attributed it to a coupling between their spin and the vorticity of the fluid created in heavy ion collisions, but how the spin comes to equilibrium with vorticity is an open problem. Recently we found that vorticity fluctuations and helicity flip of strange quarks in quark-gluon plasma through perturbative QCD processes resulted in equilibration times far too long to be relevant. Here we consider the Nambu--Jona-Lasinio model with the inclusion of the six-quark Kobayashi--Maskawa--'t Hooft interaction which breaks axial U(1). Using instanton inspired models for the temperature dependence of the axial symmetry breaking, we find that constituent strange quarks can reach spin equilibrium at temperatures below about 170 MeV, just before they hadronize to form hyperons.

arXiv comment8 pages, 3 figures. arXiv admin note: text overlap with arXiv:1907.10750

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• Topology and axions in QCD
• Hyperon Polarization from the Vortical Fluid in Low Energy Nuclear Collisions
• Spin polarization dynamics in the non-boost-invariant background
• Global spin polarization of multistrange hyperons and feed-down effect in heavy-ion collisions
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• Hyperon--anti-hyperon polarization asymmetry in relativistic heavy-ion collisions as an interplay between chiral and helical vortical effects
• Spin polarization dynamics in the Bjorken-expanding resistive MHD background
• Topological susceptibility, divergent chiral density and phase diagram of chirally imbalanced QCD medium at finite temperature
• Spin versus Helicity Equilibration Times and Lagrangian for Strange Quarks in Rotating Quark-Gluon Plasma
• The linear mode analysis and spin relaxation
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• Lectures on nonperturbative QCD ( Nonperturbative Topological Phenomena in QCD and Related Theories)
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• The Chiral Phase Transitions of Helical Matter
• QCD transition at the physical point, and its scaling window from twisted mass Wilson fermions
• Sphaleron Transition Rates and the Chiral Magnetic Effect
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