Study of charged pion elliptic flow and search for Electric Quadrupole Effect in Au+Au collisions at 39 GeV from STAR

It is predicted that Chiral Magnetic Wave (CMW) at finite baryon density can induce an electric quadrupole moment of the quark-gluon plasma produced in heavy ion collisions. [1] This electric quadrupole deformation lifts the degeneracy between the elliptic flow ($v^{2})$ of positive and negative pions leading to $v^{2}(\pi _{+}) \quad < \quad v^{2}(\pi _{-})$. We study the difference between $v^{2}(\pi _{+})$ and $v^{2}(\pi _{-})$ measurements from STAR for Au+Au collisions at 39 GeV, and investigate the dependence of the $v^{2 }$difference on the measured net-proton number of the data sample. Here the net-proton number is used to approximate the conserved net-baryon number, and the $v^{2}$ difference is expected to be proportional to the baryon number asymmetry in the presence of an Electric Quadrupole Effect. In this work, we present pion elliptic flow as a function of transverse momentum and centrality for Au+Au collisions at 39 GeV, and we will discuss the dependence of the $v^{2}$ difference on net-proton numbers. \\[4pt] [1] Y. Burnier, D. Kharzeev, J. Liao and H. Yee, arXiv:1103.1307.