Speaker
Description
The Chiral Magnetic Wave (CMW) was predicted to arise from the interplay of the chiral magnetic effect and the chiral separation effect, which can lead to the formation of electric quadrupole moment in heavy-ion collisions. This electric quadrupole moment can produce charge asymmetry dependence of the elliptic flow ($v_2$) for charged particles: $v_2(\pm) - v_2(\mp) = \mp r_{2} \times A_{\rm ch}$, where $r_{2}=\frac{q_{e}}{\hat{\rho}_{e}}$.
In this poster, we will present the STAR measurements of the slope parameter ($r_{2}$) from different colliding systems: Au+Au at 200, 54.4 and 27 GeV, Cu+Cu and Cu+Au at 200 GeV. Two approaches, Q-Cumulant ($v_2 \{2\}$ and $v_2\{4\}$) and event-plane ($v_2(EP)$) methods, are used to measure $v_2$ of $\pi^{\pm}$ at low transverse momenta in order to evaluate the non-flow contributions in the $v_2$ measurement. $v_2\{2\}$ and $v_2(EP)$ with pseudorapidity gaps can reduce the short-range non-flow contributions. $v_2\{4\}$ can suppress non-flow contributions and is believed to be more sensitive to the reaction plane (and hence the magnetic field). Thus $v_2\{4\}$ can be more sensitive to the CMW dynamics. The centrality dependence of $r_{2}$ will be compared across different collision systems and beam energies. Physics implications on the search of the CMW and the background dynamics from our systematic studies will be discussed.
