Energy and system-size dependence of two- and four-particle $v_2$ measurements in heavy-ion collisions at RHIC and their implications on flow fluctuations and nonflow

We present STAR measurements of azimuthal anisotropy by means of the two- and four-particle cumulants $v_2$ ($v_2{2}$ and $v_2{4}$) for Au+Au and Cu+Cu collisions at center of mass energies $sqrt{s_{_{mathrm{NN}}}} = 62.4$ and 200 GeV. The differencebetween $v_2{2}^2$ and $v_2{4}^2$ is related to $v_{2}$ fluctuations ($sigma_{v_2}$) and nonflow $(delta_{2})$. We present an upper limit to $sigma_{v_2}/v_{2}$. Following the assumption that eccentricity fluctuations $sigma_{epsilon}$ dominate $v_2$ fluctuations $frac{sigma_{v_2}}{v_2} approx frac{sigma_{epsilon}}{epsilon}$ we deduce the nonflow implied for several models of eccentricity fluctuations that would be required for consistency with $v_2{2}$ and $v_2{4}$. We also present results on the ratio of $v_2$ to eccentricity.