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

TL;DR

This paper develops a hydrodynamic scaling law to connect nuclear deformation with elliptic flow measurements in heavy-ion collisions, revealing a discrepancy in uranium deformation estimates between low-energy data and collider results.

Contribution

It introduces a new formula linking nuclear deformation to elliptic flow differences and applies it to experimental data, challenging existing nuclear structure knowledge.

Findings

RHIC data suggests higher uranium deformation than previously reported

The derived formula accurately relates flow differences to nuclear shape

Results pose a puzzle for nuclear phenomenology regarding uranium deformation

Abstract

In the hydrodynamic framework of heavy-ion collisions, elliptic flow, $v_2$, is sensitive to the quadrupole deformation, $\beta$, 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 $v_2$ measured between collision systems that are close in size to the value of $\beta$ of the respective species. We validate our formula in simulations of 238U+238U and 197Au+197Au collisions at top Relativistic Heavy Ion Collider (RHIC) energy, and subsequently apply it to experimental data. Using the deformation of 238U from low-energy experiments, we find that RHIC $v_2$ data implies $0.16 \lesssim |\beta| \lesssim 0.20$ for 197Au nuclei, i.e., significantly more deformed than reported in the literature, posing an interesting puzzle in nuclear phenomenology.