Speaker
Description
Nuclear deformation is an ubiqutous phenomenon for most atomic nuclei, reflecting collective motion induced by interaction between valance nucleons and shell structure. In most cases, the deformation has a quadrupole shape that is charactorized by overall strength $\beta_2$ and triaxiality $\gamma$ (prolate $\gamma=0$, obolate $\gamma=\pi/3$ and triaxial otherwise). Collisions of deformed nuclei lead to large shape and size fluctuations in the initial state geometry, which after collective expansion, lead to enhanced fluctuation of elliptic flow $v_2$ and event-by-event mean transverse momentum $[p_{\mathrm{T}}]$. Therefore, detailed study of the $v_2$, and $[p_{\mathrm{T}}]$ and correlations beween them can constrain the deformation parameters $(\beta_2,\gamma)$. A comparion of $(\beta_2,\gamma)$ with those measured from nuclear structure experiment could then be used to constrain the hydrodynamic responses of heavy-ion collisions. In this poster, we present results of $v_2$, $[p_{\mathrm{T}}]$ fluctuations and $v_2^2-[p_{\mathrm{T}}]$ correlation for harmonics $n=2,3,4$ in modestly-deformed $^{197}$Au+$^{197}$Au collisions at 200 GeV and highly-deformed $^{238}$U+$^{238}$U collisions at 193 GeV. Significant differences for mean, variance $c_2$ and skewness $c_3$ of $[p_{\mathrm{T}}]$ fluctuations, are observed between the two systems as a function of centrality. The $v_2^2-[p_{\mathrm{T}}]$ results remain positive over the full centrality in Au+Au collisions, while they change sign in 0-5\% central U+U collisions. The ratio of $v_2$ and $c_2$ between U+U and Au+Au in ultra-central collisions (UCC) are used to constrain the value of $\beta_2$, which leads to an estimate of $\beta_{2Au}\sim0.18$. On the other hand, the value of $\gamma$ can be constrained from the ratios of $v_2^2-[p_{\mathrm{T}}]$ and $c_3$ between U+U and Au+Au. The enhancement of $c_3$ and the suppression of $v_2^2-[p_{\mathrm{T}}]$ in UCC confirm that Uranum is prolate deformed with $\gamma\sim0$. Comparison with state-of-art model calculations is discussed.
