Abstract: Centrality dependence of unidentified charged hadron v2 with respect to the first harmonic ZDC-SMD event plane in Au + Au at = 200 GeV

One of the most striking results is the large elliptic flow ($v_2$) at RHIC. Detailed mass and transverse dependence of elliptic flow are well described by ideal hydrodynamic calculations for $p_T < $ 1 GeV/c, and by parton coalescence/recombination picture for $p_T = 2 - 6$ GeV/c. The systematic error on $v_2$ is dominated by so-called "non-flow effects", which is the correlation not originated from reaction plane. It is crucial to understand and reduce the systematic error from non-flow effects in order to understand the underlying collision dynamics. In this talk, we present the centrality dependence of unidentified hadron $v_2$ with respect to the first harmonic event plane at ZDC-SMD in Au + Au collisions at = 200 GeV. Large rapidity gap ($|Deltaeta| > 6$) between midrapidity and ZDC could enable us to minimize possible non-flow contributions. We compare the results of with which is measured by event plane determined at $|eta| = 3.1 - 3.9$. Possible non-flow contributions in those results will be discussed.