Imaging the initial condition of heavy-ion collisions and nuclear structure across the nuclide chart

High-energy nuclear collisions encompass three key stages: the structure of the colliding nuclei, informed by low-energy nuclear physics, the <em>initial condition</em>, leading to the formation of quark–gluon plasma (QGP), and the hydrodynamic expansion and hadronization of the QGP, leading to final-state hadron distributions that are observed experimentally. Recent advances in both experimental and theoretical methods have ushered in a precision era of heavy-ion collisions, enabling an increasingly accurate understanding of these stages. However, most approaches involve simultaneously determining both QGP properties and initial conditions from a single collision system, creating complexity due to the coupled contributions of these stages to the final-state observables. To avoid this, we propose leveraging established knowledge of low-energy nuclear structures and hydrodynamic observables to independently constrain the QGP’s initial condition. By conducting comparative studies of collisions involving isobar-like nuclei—species with similar mass numbers but different ground-state geometries—we can disentangle the initial condition’s impacts from the QGP properties. This approach not only refines our understanding of the initial stages of the collisions but also turns high-energy nuclear experiments into a precision tool for imaging nuclear structures, offering insights that complement traditional low-energy approaches. Opportunities for carrying out such comparative experiments at the Large Hadron Collider and other facilities could significantly advance both high-energy and low-energy nuclear physics. Additionally, this approach has implications for the future electron-ion collider. While the possibilities are extensive, we focus on selected proposals that could benefit both the high-energy and low-energy nuclear physics communities. Originally prepared as input for the long-range plan of U.S. nuclear physics, this white paper reflects the status as of September 20. Authors: Jia, Jiangyong [Stony Brook Univ., NY (United States); Brookhaven National Laboratory (BNL), Upton, NY (United States)]; Giacalone, Giuliano [European Organization for Nuclear Research (CERN), Geneva (Switzerland)]; Bally, Benjamin [Univ. Paris-Saclay, Gif-sur-Yvette (France); Alternative Energies and Atomic Energy Commission (CEA) (France)]; Brandenburg, James Daniel [The Ohio State Univ., Columbus, OH (United States)]; Heinz, Ulrich [The Ohio State Univ., Columbus, OH (United States)]. DOE Contract: AC02-05CH11231; FG02-07ER41521; FG02-89ER40531; SC0004286; SC0005131; SC0011088; SC0012704; SC0013365; SC0023175; SC0023861; SC0024232; SC0024586; SC0024602. Subjects: 73 NUCLEAR PHYSICS AND RADIATION PHYSICS