Elliptic flow fluctuations in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV

We report first measurements of elliptic flow ($v_2$) fluctuations for the STAR collaboration at middle rapidity in $\sqrt{s_{_{NN}}}=200$ GeV Au+Au collisions. We analyze the multiplicity dependence of the flow vector length distribution to disentangle non-flow correlations from $v_2$ fluctuations. We find that the width of the $v_2$ distribution is approximately 36% of the mean $v_2$ and, within errors, independent of collision centrality. This value coincides with eccentricity fluctuations, apparently leaving little room for other sources of fluctuations.