In heavy ion collisions, elliptic flow $v_2$ and radial flow, characterized by eventwise average transverse momentum $\left[p_{\mathrm{T}}\right]$, 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 $\left[p_{\mathrm{T}}\right], {\rho }_2$, was found to be particularly sensitive to the quadrupole deformation parameter $\beta$ that is traditionally measured in low energy experiments. Built on earlier insight that the prolate deformation $\beta >0$ reduces the ${\rho }_2$ in ultracentral collisions (UCC), we show that the prolate deformation $\beta <0$ enhances the value of ${\rho }_2$. As $\beta >0$ and $\beta <0$ are the two extremes of triaxiality, the strength and sign of $v_2^2\text{−}\left[p_{\mathrm{T}}\right]$ 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 ($<{10}^{-24}\mathrm{s}$).

• Received 12 May 2021
• Revised 20 September 2021
• Accepted 30 September 2021

DOI:https://doi.org/10.1103/PhysRevC.105.014906