Local spin polarizations in relativistic heavy ion collisions

• Published in: arXiv.org 2020-02
• Main Authors: Liu, Shuai Y F, Sun, Yifeng, Ko, Che Ming
• Format: Article
• Language: English
• Subjects: Angular momentum; Atomic collisions; Charge distribution; Fermions; Heavy ions; Hyperons; Ionic collisions; Polarization (spin alignment); Quarks; Relativism; Relativistic effects; Rotating matter; Spin-orbit interactions; Vorticity
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2002.11752

Based on a generalized side-jump formalism for massless chiral fermions, which naturally takes into account the spin-orbit coupling in the scattering of two chiral fermions and the chiral vortical effect in a rotating chiral fermion matter, we have developed a covariant and total angular momentum conserved chiral transport model to study both the global and local polarizations of this matter. For a system of massless quarks of random spin orientations and finite vorticity in a box, we have demonstrated that the model can exactly conserve the total angular momentum of the system and dynamically generate the quark spin polarization expected from a thermally equilibrated quark matter. Using this model to study the spin polarization in relativistic heavy-ion collision, we have found that the local quark spin polarizations depend strongly on the reference frame where they are evaluated as a result of the nontrivial axial charge distribution caused by the chiral vortical effect. We have further shown that because of the anomalous orbital or side-jump contribution to the quark spin polarization, the local quark polarizations calculated in the medium rest frame are qualitatively consistent with the local polarizations of Lambda hyperons measured in experiments.