  The elliptic flow splitting between particles and their antiparticles has
recently been observed by the STAR Collaboration in the beam-energy scan
program at the Relativistic Heavy Ion Collider. In studies based on transport
models, we have found that this splitting can be explained by the different
mean-field potentials acting on particles and their antiparticles in the
produced baryon-rich matter. In particular, we have shown that the
experimentally measured relative elliptic flow difference can help constrain
the vector coupling constant in the Nambu-Jona-Lasinio model used in describing
the partonic stage of heavy-ion collisions. This information is useful for
locating the critical point in the QCD phase diagram and thus understanding the
phase structure of QCD.
