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Shear-Induced Spin Polarization in Heavy-Ion Collisions.
Baochi Fu1,2, Shuai Y F Liu3, Longgang Pang4
1Department of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China.
Physical Review Letters
|October 15, 2021
Summary
We discovered shear-induced polarization (SIP) from fluid gradients in heavy-ion collisions. This new effect, alongside thermal vorticity, explains experimental spin polarization data, with SIP often dominating.
Area of Science:
- High-energy nuclear physics
- Quantum field theory
- Condensed matter physics
Background:
- Hydrodynamic gradients in heavy-ion collisions generate spin polarization.
- Thermal vorticity effects are well-studied contributors to spin polarization.
Purpose of the Study:
- To identify and quantify new sources of spin polarization beyond thermal vorticity.
- To investigate the role of fluid shear in generating spin polarization.
Main Methods:
- Utilized quantum kinetic equations and linear response theory to derive shear-induced polarization (SIP).
- Employed a realistic hydrodynamic model for noncentral heavy-ion collisions at $\sqrt{s_{NN}}=200$ GeV.
- Calculated differential spin polarization along beam (z) and out-of-plane (y) directions.
Main Results:
- Identified shear-induced polarization (SIP) as a novel contribution to spin polarization.
- SIP exhibits the same azimuthal angle dependence as experimental data.
- SIP competes with thermal vorticity effects, and in certain scenarios, it dominates.
Conclusions:
- SIP is a significant factor in understanding spin polarization in heavy-ion collisions.
- The interplay between SIP and thermal vorticity explains observed spin polarization patterns.
- SIP's dominance in specific scenarios aligns with experimental findings for Λ polarization.
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