Polarization probes of vorticity in heavy ion collisions

Abstract

We discuss the information that can be deduced from a measurement of particle (hyperon or vector meson) polarization in ultrarelativistic nuclear collisions. We describe the sensitivity of polarization to initial conditions, hydrodynamic evolution and mean free path, and find that the polarization observable is sensitive to all details and stages of the system's evolution. We suggest that an experimental investigation covering production plane and reaction plane polarizations, as well as the polarization of jet-associated particles in the plane defined by the jet and particle direction, can help in disentangling the factors contributing to this observable. Scans of polarization in energy and rapidity might also point to a change in the system's properties.Comment: In press, Phys.Rev.C. One new figure, text streamlined and edited, physics conclusions and reasoning not change

Polarization of massive fermions in a vortical fluid

“…The vorticity induced by global orbital angular momentum in the fluid can be considered as local rotational motion of particles [3,4,7,8]. It is closely related to the rapidity dependence of the v 1 flow and shear of the longitudinal flow velocity inside the reaction plane [5,9,10].…”

“…In non-central high-energy heavy-ion collisions, the large orbital angular momentum present in the colliding system can lead to non-vanishing local vorticity in the hot and dense fluid [1][2][3][4][5][6]. The vorticity induced by global orbital angular momentum in the fluid can be considered as local rotational motion of particles [3,4,7,8].…”

Pseudoscalar condensation induced by chiral anomaly and vorticity for massive fermions

“…The CME, CVE and other related effects such as chiral magnetic wave [15,16] have been extensively studied in the quark-gluon plasma produced in high-energy heavy-ion collisions in which very strong magnetic fields [5,[17][18][19][20][21][22][23][24][25] and huge global angular momenta [26][27][28][29] are produced in non-central collisions. The charge separation effect observed in STAR [30,31] and ALICE [32] experiments are consistent to the CME prediction.…”

Quark polarization in a viscous quark-gluon plasma

“…Since interaction via one-gluon exchange in QCD contains a spinorbital coupling, the OAM could cause a global spinpolarization of quarks and anti-quarks in the direction parallel to the OAM. Such a global (anti-)quark polarization should have many observable consequences such as global hyperon polarization [12,13], vector meson spin alignment [12,14] and the emission of circularly polarized photons [15]. Predictions have been made [12,[14][15][16][17] for these measurable quantities as functions of the global quark polarization P q .…”