  We argue that measurements of identified-particle elliptic flow in a wide
energy range could shed light on the possible phase change in high-energy heavy
ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC). When the
hadronization process is dominated by quark coalescence, the
number-of-constituent-quark (NCQ) scaling for the identified-particle elliptic
flow can serve as a probe for studying the strong interacting partonic matter.
In the upcoming RHIC low-energy runs, the NCQ scaling behavior may be broken
because of the change of the effective degrees of freedom of the hot dense
matter, which corresponds to the transition from the dominant partonic phase to
the dominant hadronic phase. A multiphase transport model is used to present
the dependence of NCQ scaling behavior on the different hadronization
mechanisms.
