Impact of Nuclear Deformation on Relativistic Heavy-Ion Collisions: Assessing Consistency in Nuclear Physics across Energy Scales

In the hydrodynamic framework of heavy-ion collisions, elliptic flow v2 is sensitive to the quadrupole deformation β of the colliding ions. This enables one to test whether the established knowledge on the low-energy structure of nuclei is consistent with collider data from high-energy experiments. We derive a formula based on generic scaling laws of hydrodynamics to relate the difference in v2 measured between collision systems that are close in size to the value of β of the respective species. We validate our formula in simulations of U238+U238 and Au197+Au197 collisions at top Relativistic Heavy Ion Collider (RHIC) energy, and subsequently apply it to experimental data. Using the deformation of U238 from low-energy experiments, we find that RHIC v2 data implies 0.16≲|β|≲0.20 for Au197 nuclei, i.e., significantly more deformed than reported in the literature, posing an interesting issue in nuclear phenomenology.