Charge dependent mixed-harmonic correlations relative to the reaction plane
in Au+Au collisions at 200 GeV at RHIC/STAR

In the chiral magnetic effect (CME) [1], an electric current is induced
in the presence of a strong magnetic field and a chirality imbalance in
the medium created in high-energy nuclear collisions. One corresponding 
observable for the charge separation across the reaction plane ($\psi$) 
is the charge dependent two-particle azimuthal correlator, 
$\gamma_{112}= <cos(\phi_1 + \phi_2 - 2\psi)>$.
However, the $\gamma_{112}$ contains both the CME signal and the flow background,
complicating the interpretation of the data. In this poster, we
investigate the background mechanism with a modified mixed-harmonic correlator,
$\gamma_{132} = <cos(\phi_1 - 3\phi_2 + 2\psi)>$. The $\gamma_{132}$ only 
contains the background, and reflects the role played by the collective flow 
in the original $\gamma_{112}$ correlator. We will present the STAR data of
$\gamma_{132}$ as a function of centrality measured in Au+Au collisions 
at 200 GeV. The results will be compared with model calculations. 
The physics implications will be discussed.

[1]D. Kharzeev, Phys. Lett. B 633 (2006) 260.