Constraining nuclear quadrupole deformation from correlation of elliptic flow and transverse momentum in heavy ion collisions

In heavy ion collisions, elliptic flow v2 and radial flow, characterized by event-wise average transverse momentum [pT], 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 v2 and [pT], ρ2, was found to be particularly sensitive to the quadrupole deformation parameter β that is traditionally measured in low energy experiments. Built on earlier insight that the prolate deformation β > 0 reduces the ρ2 in ultra-central collisions (UCC), we show that the prolate deformation β < 0 enhances the value of ρ2. As β > 0 and β < 0 are the two extremes of triaxiality, the strength and sign of v 2 − [pT] 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 time scale (< 10s).