Precision Determination of the Neutral Weak Form Factor of ^{48}Ca

Determination of the Neutron Skin of ^{208}Pb from Ultrarelativistic Nuclear Collisions

Emergent bulk properties of matter governed by the strong nuclear force give rise to physical phenomena across vastly different scales, ranging from the shape of atomic nuclei to the masses and radii of neutron stars. They can be accessed on Earth by measuring the spatial extent of the outer skin made of neutrons that characterizes the surface of heavy nuclei. The isotope ^{208}Pb, owing to its simple structure and neutron excess, has been in this context the target of many dedicated efforts. Here, we determine the neutron skin from measurements of particle distributions and their collective flow in ^{208}Pb+^{208}Pb collisions at ultrarelativistic energy performed at the Large Hadron Collider, which are mediated by interactions of gluons and thus sensitive to the overall size of the colliding ^{208}Pb ions. By means of state-of-the-art global analysis tools within the hydrodynamic model of heavy-ion collisions, we infer a neutron skin Δr_{np}=0.217±0.058  fm, consistent with nuclear theory predictions, and competitive in accuracy with a recent determination from parity-violating asymmetries in polarized electron scattering. We establish thus a new experimental method to systematically measure neutron distributions in the ground state of atomic nuclei.

Energy-Density Modeling of Strongly Interacting Matter: Atomic Nuclei and Dense Stars

We seek a simple but physically motivated model of strongly interacting matter applicable in atomic nuclei and the dense matter in the core of neutron stars. For densities below and somewhat above normal nuclear density, energy density functional (EDF) theory based on nucleonic degrees of freedom is the ideal candidate. We have explored that direction within the KIDS (Korea-IBS-Daegu-SKKU) framework, which we review in this contribution. The formalism for the KIDS-EoS and microscopic KIDS-EDF and optimization options for the EDF are described in a practical way to facilitate further applications. At densities higher than one nucleon per single-nucleon volume, i.e., roughly 0.4 fm−3, nucleonic degrees of freedom are no longer appropriate. The pseudo-conformal symmetry emergent in dense, topologically altered nuclear matter provides a simple expression for the energy per baryon in terms of the baryonic density. Besides resembling a simple EDF for dense matter, the expression has the appeal that it predicts a converged speed of sound at high densities. It can thus be implemented as a special case of the constant speed of sound (CSS) model. Here we consider a matching between representative nucleonic KIDS-EoSs and the CSS model, including the pseudo-conformal EoS, and apply the unified model to describe the mass–radius relation of neutron stars and examine the compatibility of CSS cores with heavy neutron stars. Although an abrupt transition to the pseudo-conformal regime at low densities does not favor heavy neutron stars, intermediate scenarios including a cusp in the speed of sound are not ruled out, while some appear more favorable to heavy stars than purely nucleonic matter.

Trends of Neutron Skins and Radii of Mirror Nuclei from First Principles

The neutron skin of atomic nuclei impacts the structure of neutron-rich nuclei, the equation of state of nucleonic matter, and the size of neutron stars. Here we predict the neutron skin of selected light- and medium-mass nuclei using coupled-cluster theory and the auxiliary field diffusion Monte Carlo method with two- and three-nucleon forces from chiral effective field theory. We find a linear correlation between the neutron skin and the isospin asymmetry in agreement with the liquid-drop model and compare with data. We also extract the linear relationship that describes the difference between neutron and proton radii of mirror nuclei and quantify the effect of charge symmetry breaking terms in the nuclear Hamiltonian. Our results for the mirror-difference charge radii and binding energies per nucleon agree with existing data.

Hadron production from heavy ion collisions

A brief review of some topics in hadron production from heavy ion collisions is given. They include charged pion ratio as a probe of nuclear symmetry energy, in-medium effects on pion production, en- hanced Λc/D0 ratio, Λ local polarization, and X(3872) production.

Combined Theoretical Analysis of the Parity-Violating Asymmetry for ^{48}Ca and ^{208}Pb

The recent experimental determination of the parity violating asymmetry A_{PV} in ^{48}Ca and ^{208}Pb at Jefferson Lab is important for our understanding on how neutrons and protons arrange themselves inside the atomic nucleus. To better understand the impact of these measurements, we present a rigorous theoretical investigation of A_{PV} in ^{48}Ca and ^{208}Pb and assess the associated uncertainties. We complement our study by inspecting the static electric dipole polarizability in these nuclei. The analysis is carried out within nuclear energy density functional theory with quantified input. We conclude that the simultaneous accurate description of A_{PV} in ^{48}Ca and ^{208}Pb cannot be achieved by our models that accommodate a pool of global nuclear properties, such as masses and charge radii, throughout the nuclear chart, and describe-within one standard deviation-the experimental dipole polarizabilities α_{D} in these nuclei.

Ab initio predictions link the neutron skin of 208Pb to nuclear forces

Heavy atomic nuclei have an excess of neutrons over protons, which leads to the formation of a neutron skin whose thickness is sensitive to details of the nuclear force. This links atomic nuclei to properties of neutron stars, thereby relating objects that differ in size by orders of magnitude. The nucleus 208Pb is of particular interest because it exhibits a simple structure and is experimentally accessible. However, computing such a heavy nucleus has been out of reach for ab initio theory. By combining advances in quantum many-body methods, statistical tools and emulator technology, we make quantitative predictions for the properties of 208Pb starting from nuclear forces that are consistent with symmetries of low-energy quantum chromodynamics. We explore 109 different nuclear force parameterizations via history matching, confront them with data in select light nuclei and arrive at an importance-weighted ensemble of interactions. We accurately reproduce bulk properties of 208Pb and determine the neutron skin thickness, which is smaller and more precise than a recent extraction from parity-violating electron scattering but in agreement with other experimental probes. This work demonstrates how realistic two- and three-nucleon forces act in a heavy nucleus and allows us to make quantitative predictions across the nuclear landscape.