Systematic investigation of azimuthal anisotropy in Au+Au and U+U collisions at s NN = 200 GeV

We present a study of azimuthal anisotropy parameter (vn) of produced particles in Au+Au and U+U collisions at top RHIC collision energy. The U+U collisions have been studied with and without including the deformed shape of the uranium nuclei. For this purpose, we have used a multi-phase transport (AMPT) model that includes the implementation of deformed uranium nuclei. It is found that the elliptic flow (v2) is higher in central U+U collisions with deformed uranium nuclei compared to Au+Au and spherical U+U. On the other hand, other higher harmonics (v3, v4, and v5) are found to be almost similar in magnitude for all three systems (Au+Au, deformed U+U, and spherical U+U). We have shown that the magnitude of v2/ϵ2 is higher (similar) in Au+Au collisions compared to deformed (spherical) U+U collisions at most central collisions. However, we believe v2/ϵ2 reflect true collectivity and more collectivity is expected in large nuclei (U235) compared to the small Au197 nucleus. This indicates that in the case of deformed nuclei, eccentricity (ϵ2) scaled v2 may not reflect true collectivity. On the other hand, magnitudes of v3/ϵ3, v4/ϵ4 and v5/ϵ5 for a given centrality are the same for Au+Au, deformed U+U, and spherical U+U collisions. These are interesting observations and can be checked in experimental data at RHIC. We have also compared Au+Au and U+U results with that of Cu+Cu for a better understanding of our findings.