Signatures of a baryonic spin-Hall effect in dense QCD matter

Recent theoretical analyses show that spin current can be induced by the baryon chemical potential gradient ∇ μ B which becomes sizable in the fireballs created in heavy-ion collisions (HIC) at a beam energy of O ( 10 ) GeV. This spin transport phenomenon can be considered as the cousin effect of the spin-Hall effect (SHE) in condensed matter systems with ∇ μ B playing the role of the analogous electric field. In this letter, we study this important mechanism, which we call “baryonic SHE” or ∇ μ B -induced polarization ( ∇ μ B -IP), for differential spin polarization generation that has not been systematically explored before. We predict the signature of the baryonic SHE in HIC using a ( 3 + 1 ) D viscous hydrodynamic model MUSIC with a multiphase transport initial condition. We propose to use the second Fourier coefficients of the net spin polarization of Λ hyperon as sensitive probes for the baryonic SHE. Those baryonic SHE observables show a qualitative difference in sign and beam energy dependence for the situations with and without the baryonic SHE. Future experimental observation of these distinct qualitative features would provide strong evidence for the existence of this “baryonic SHE” in the hot and dense quantum chromodynamics matter.