Probing nuclear quadrupole deformation from correlation of elliptic flow and transverse momentum in heavy ion collisions
J. Jia, S. Huang, C. Zhang
Abstract
In heavy ion collisions, elliptic flow ${v}_{2}$ and radial flow, characterized by eventwise average transverse momentum $[{p}_{\mathrm{T}}]$, are related to the shape and size of the overlap region, which are sensitive to the shape of colliding atomic nuclei. The Pearson correlation coefficient between ${v}_{2}$ and $[{p}_{\mathrm{T}}], {\ensuremath{\rho}}_{2}$, was found to be particularly sensitive to the quadrupole deformation parameter $\ensuremath{\beta}$ that is traditionally measured in low energy experiments. Built on earlier insight that the prolate deformation $\ensuremath{\beta}>0$ reduces the ${\ensuremath{\rho}}_{2}$ in ultracentral collisions (UCC), we show that the prolate deformation $\ensuremath{\beta}<0$ enhances the value of ${\ensuremath{\rho}}_{2}$. As $\ensuremath{\beta}>0$ and $\ensuremath{\beta}<0$ are the two extremes of triaxiality, the strength and sign of ${v}_{2}^{2}\text{\ensuremath{-}}[{p}_{\mathrm{T}}]$ correlation can be used to provide valuable information on the triaxiality of the nucleus. Our study provide further arguments for using the hydrodynamic flow as a precision tool to directly image the deformation of the atomic nuclei at extremely short timescale ($<{10}^{\ensuremath{-}24}\phantom{\rule{0.28em}{0ex}}\mathrm{s}$).