Extraction of ground-state nuclear deformations from ultra-relativistic heavy-ion collisions: Nuclear structure physics context

TL;DR

The paper critically examines the premise that ultra-relativistic heavy-ion collisions can image ground-state nuclear deformations. It shows that for a ground state with $J^\pi=0^+$ the intrinsic shape is not directly accessible and that observable deformation information requires conditional two- or three-body densities rather than one-body densities; it argues that instantaneous shapes and zero-point fluctuations in 'shape' are not physical for stationary eigenstates. It surveys the rich low-energy deformation data (e.g., quadrupole moments $Q$, deformation parameters $\beta_2$, $\beta_3$) and cautions that UHIC results must be anchored to this database with rigorous uncertainty quantification across the full multistage pipeline. The work concludes that UHIC presently offers limited direct constraints on nuclear shapes but valuable insight into many-body correlations, provided modeling uncertainties are carefully controlled and cross-validated against established nuclear-structure observables.

Abstract

The collective-flow-assisted nuclear shape-imaging method in ultra-relativistic heavy-ion collisions has recently been used to characterize nuclear collective states. In this paper, we assess the foundations of the shape-imaging technique employed in these studies. We argue that some current UHIC nuclear imaging techniques neglect fundamental aspects of spontaneous symmetry-breaking and symmetry-restoration in colliding ions and incorrectly infer one-body multipole moments from studies of nucleonic correlations. Therefore, the impact of this approach on nuclear structure research has been overstated. Conversely, efforts to incorporate existing knowledge on nuclear shapes into analysis pipelines can be beneficial for benchmarking tools and calibrating models used to extract information from ultra-relativistic heavy-ion experiments.