Abstract
We argue that the enhancement in the spin polarization of anti-hyperons compared to the polarization of the hyperons in noncentral relativistic heavy-ion collisions arises as a result of an interplay between the chiral and helical vortical effects. The chiral vortical effect generates the axial current of quarks along the vorticity axis while the recently found helical vortical effect generates the helicity flow – the projection of the quark’s polarization vector onto its momentum – along the same axis. For massless fermions, the helical charge corresponds to a difference in the contributions of particles and anti-particles to the axial charge. Assuming that the spin of light quarks transfers to the strange quarks via the vector kaon states (“the spin-vector dominance”), we are able to describe the ratio of the (anti)hyperon spin polarizations, obtained by the STAR group, without fitting parameters. We also argue that the helical vortical effect dominates over the chiral vortical effect and the chiral magnetic effect in the generation of the electric current.
Highlights
Over the past decades, the experiments of relativistic heavy ion collisions at RHIC and LHC have served as an excellent arena to study the properties of quantum matter in extreme conditions
We argue that the enhancement in the spin polarization of anti-hyperons compared to the polarization of the hyperons in noncentral relativistic heavy-ion collisions arises as a result of an interplay between the chiral and helical vortical effects
We have shown that the interplay of axial and helical vortical effects allows us to compute, separately, the spin polarizations of light quarks and light anti-quarks along the global vorticity axis in noncentral collisions
Summary
The spin-orbit coupling, inherent in the Dirac equation, leads to a polarization of the fermion spins with respect to the direction of the collective angular momentum. The transport consequences of this effect were highlighted more than four decades ago by Vilenkin, who pointed out that rotating (Kerr) black holes generate a net neutrino current directed along the axis parallel to the black hole’s angular momentum [11,12,13]. This phenomenon constitutes one of the chiral vortical effects which were later understood in the framework of anomalous hydrodynamics of relativistic vortical fluids [14].
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