Searching for the subatomic swirls in the CuCu and CuAu collisions

Abstract

Recently the STAR Collaboration reported measurement of the “subatomic swirls”, that is, the most vortical fluid flow structures in the quark–gluon plasma produced via the AuAu collisions at the Relativistic Heavy Ion Collider (RHIC). This result has attracted significant interest and generated wide enthusiasm. For such an important finding, it is crucial to look for additional evidences of confirmation and to critically test the current interpretation of the global polarization measurement. We suggest that the CuCu and CuAu colliding systems at RHIC provide such opportunity. Interestingly, our calculations reveal that the fluid vorticity in the CuCu or CuAu collision is comparable to that in the AuAu collision. We find the computed Λ hyperon polarization effect is stronger in the CuCu and CuAu systems than the AuAu system at the same collisional beam energy and centrality class, with an interesting hierarchy CuCu > CuAu > AuAu due to interplay between Λ production timing and the time evolution of the vorticity. These predictions can be readily tested by experimental data.