The impact of nuclear deformation on relativistic heavy-ion collisions:\n assessing consistency in nuclear physics across energy scales

Abstract

In the hydrodynamic framework of heavy-ion collisions, elliptic flow, $v_2$,\nis sensitive to the quadrupole deformation, $\\beta$, of the colliding ions.\nThis enables one to test whether the established knowledge on the low-energy\nstructure of nuclei is consistent with collider data from high-energy\nexperiments. We derive a formula based on generic scaling laws of hydrodynamics\nto relate the difference in $v_2$ measured between collision systems that are\nclose in size to the value of $\\beta$ of the respective species. We validate\nour formula in simulations of 238U+238U and 197Au+197Au collisions at top\nRelativistic Heavy Ion Collider (RHIC) energy, and subsequently apply it to\nexperimental data. Using the deformation of 238U from low-energy experiments,\nwe find that RHIC $v_2$ data implies $0.16 \\lesssim |\\beta| \\lesssim 0.20$ for\n197Au nuclei, i.e., significantly more deformed than reported in the\nliterature, posing an interesting puzzle in nuclear phenomenology.\n