Energy Dependence of the \textit{v}$_{2}$ scaling and the QCD Phase Boundary

In high-energy nuclear collisions at RHIC ($s_{NN}$\textit{ = 60 -- 200 GeV}), the quark coalescence has been identified as the process for hadronization. As a result, one observes a scaling in elliptic flow parameter \textbf{\textit{v}}$_{2}$ [1,2] and hadron type dependence (within 2 $<$ p$_{T} \quad <$ 5 GeV/c region) in nuclear modification parameter \textbf{\textit{R}}$_{AA}$ [1]. In a given collision when the center of mass energy is not sufficiently high to create partonic matter, one would not expect the scaling in the final observed \textbf{\textit{v}}$_{2}$. Hence, the scaling provides us a sensitive tool in order to search for the possible phase boundary in the hot/dense matter dominated by either partonic or hadronic degrees of freedom. In this talk, we will report the results from analyzing the energy dependence of \textbf{\textit{v}}$_{2}$ for identified hadrons from Au+Au collisions for energy ranging from 200 GeV to 5 GeV. Data from transport models are used in our analysis. Without the partonic coalescence, the scaling is absent.\\[4pt] [1] J. Adams, \textit{et al.,} (STAR Collaboration), Nucl. Phys. \underline {\textbf{A757}}, 102(2005).\\[0pt] [2] B.I. Abelev, \textit{et al.,} (STAR Collaboration), Phys. Rev. Lett. \underline {\textbf{99}}, 112301(2007).