Azimuthal Anisotropy Measurements by STAR

Abstract

The recent study of centrality and transverse momentum ($p_{T}$) dependence of inclusive charged hardron elliptic anisotropy ($v_{2}$) at midrapidity ($|\eta|<1.0$) in Au+Au collision at $\sqrt{s_{NN}} =$ 7.7, 11.5, 19.6, 27, and 39 GeV in STAR Beam Energy Scan program is presented. We show that the observed increase of inclusive $v_{2}$ is mainly due to the average $p_{T}$ increase with energy. In Au+Au 200 GeV collisions, the triangular anisotropy ($v_{3}$) measurements highly depend on measurment methods; $v_{3}$ is strongly dependent on $\Delta\eta$. The difference between two- and four-particle cumulants $v_{2}\lbrace{2}\rbrace$ and $v_{2}\lbrace{4}\rbrace$ for Au+Au and Cu+Cu collision at $\sqrt{s_{NN}} = $ 62.4 and 200 GeV is used to explore flow fluctuations. Furthermore, by exploiting the symmetry of average flow in pseudorapidity $\eta$ about mid-rapidty, the $\Delta\eta$-dependent and independent components are seperated using $v_{2}\lbrace2\rbrace$ and $v_{2}\lbrace{4}\rbrace$.