Systematic investigation of azimuthal anisotropy in Au+Au and U+U collisions at $\sqrt{s_{NN}}=200GeV$

We present a study of azimuthal anisotropy parameter (v _n) 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 (v ₂) 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 (v ₃, v ₄, and v ₅) 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 v ₂/ϵ ₂ is higher (similar) in Au+Au collisions compared to deformed (spherical) U+U collisions at most central collisions. However, we believe v ₂/ϵ ₂ 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 (ϵ ₂) scaled v ₂ may not reflect true collectivity. On the other hand, magnitudes of v ₃/ϵ ₃, v ₄/ϵ ₄ and v ₅/ϵ ₅ 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. (paper)