Nuclear dynamics and reactions in the ab initio symmetry-adapted framework

We review the ab initio symmetry-adapted (SA) framework for determining the structure of stable and unstable nuclei, along with related electroweak, decay, and reaction processes. This framework utilizes the dominant symmetry of nuclear dynamics, the shape-related symplectic Sp(3, R) symmetry, which has been shown to emerge from first principles and to expose dominant degrees of freedom that are collective in nature, even in the lightest species or seemingly spherical states. This feature is illustrated for a broad scope of nuclei ranging from helium to titanium isotopes, enabled by recent developments of the ab initio SA no-core shell model expanded to the continuum through the use of the SA basis and that of the resonating group method. The review focuses on energies, electromagnetic transitions, quadrupole and magnetic moments, radii, form factors, and response function moments for ground-state rotational bands and giant resonances. The method also determines the structure of reaction fragments that is used to calculate decay widths and α-capture reactions for simulated X-ray burst abundance patterns, as well as nucleon–nucleus interactions for cross sections and other reaction observables

New Ab Initio Approach to Nuclear Reactions Based on the Symmetry-Adapted No-Core Shell Model

We present the current development of a new ab initio approach for nuclear reactions that takes advantage of SU(3) symmetry and its relevant dynamics combined with the resonating group method. In this model, the structure of the clusters is based on the ab initio symmetry-adapted no-core shell model, which enables the description of spatially enhanced nuclear configurations. We will present the formalism that involves the expression of the norm kernels in the SU(3) symmetry-adapted basis, in addition to first results for the p-(formula presented), p-(formula presented)O and p-(formula presented)Ne scattering reactions

New Symmetry-Adapted ab initio Approach to Nuclear Reactions for Intermediate-mass Nuclei

With a view toward describing reactions of intermediate-mass nuclei from first principles, we present first results for the norm and Hamiltonian overlaps (kernels) for the p-α, p-16O, and p-20Ne cluster systems using realistic nucleon–nucleon interactions. This is achieved in the framework of a new ab initio approach that combines the symmetry-adapted no-core shell model (SA-NCSM) with the resonating group method (RGM). In this model, a physically relevant basis based on the SU(3) symmetry is used. The structure of the clusters is provided by the ab initio SA-NCSM, which enables the description of spatially enhanced nuclear configurations and heavier nuclei, by exploiting symmetries known to dominate in nuclei. Here, we discuss the applicability and efficacy of this approach

An above-barrier narrow resonance in F-15

Intense and purified radioactive beam of post-accelerated O-14 was used to study the low-lying states in the unbound F-15 nucleus. Exploiting resonant elastic scattering in inverse kinematics with a thick target, the second excited state, a resonance at E-R = 4.757(6)(10) MeV with a width of Gamma = 36(5)(14) keV was measured for the first time with high precision. The structure of this narrow above-barrier state in a nucleus located two neutrons beyond the proton drip line was investigated using the Gamow Shell Model in the coupled channel representation with a C-12 core and three valence protons. It is found that it is an almost pure wave function of two quasi-bound protons in the 2s(1/2) shell. (C) 2016 The Authors. Published by Elsevier B.V

Réactions nucléaires dans le modèle en couches de Gamow et solutions de l’Hamiltonien d’appariement basées sur le modèle rationnel de Gaudin

Moving towards drip lines, or higher in excitation energy, the continuum coupling becomesgradually more important, changing the nature of weakly bound states. In this regime, atomicnuclei are open quantum systems which can be conveniently described using the Gamow shellmodel (GSM) which offers a fully symmetric treatment of bound, resonance and scattering states.The understanding of specific nuclear properties is often improved by considering exactly solvablemodels, motivated by a symmetry of the many-body system. In the first part , we havegeneralized the rational Gaudin pairing model to include the continuous part of the single-particlespectrum, and then derived a reliable algebraic solution which generalizes the exact Richardsonsolution for bound states. These generalized Richardson solutions have been applied for the descriptionof binding energies and spectra in the long chain of carbon isotopes.In the second part, we have formulated the reaction theory rooted in GSM. For that theGSM is expressed in the basis of reaction channels and generalized for multi-nucleon projectiles.This reaction theory respects the antisymmetrization of target and projectile wave functions, aswell as the wave function of the combined system. The application of this theory have beenpresented for the reaction 14O(p,p’)14O, where the combined system 15F is a proton emitter, andfor 40Ca(d,d)40Ca.Au voisinage de la limite de stabilité, ou à haute énergie d’excitation, l’influence du continuumdevient de plus en plus importante, modifiant ainsi la structure des états faiblement liés. Danscette région, les noyaux sont des systèmes quantiques ouverts qui peuvent être décrits correctementavec le Gamow Shell Model (GSM) offrant une description unifiée des états liés, des résonances etdes états de diffusion.La compréhension de propriétés nucléaires induites par certaines symétries du système àplusieurs corps, peut être approfondie en considérant des modèles exactement solubles. Dansla première partie, nous avons généralisé l’Hamiltonien d’appariement basé sur le modèle rationelde Gaudin aux états du continuum, et dérivé la solution algébrique qui généralise la solution exactede Richardson initialement introduite pour les systèmes liés. Ces équations de Richardsongénéralisées ont ensuite été appliquées à l’étude des spectres et des énergies de liaison dans unechaîne d’isotopes de carbone.Dans la deuxième partie, nous avons formulé une théorie des réactions basée sur le GSM. Dansce but, le GSM est formulé dans une base de canaux de réaction pour les projectiles à plusieursnucléons. Cette théorie des réactions prend en compte l’antisymétrisation des fonctions d’onde decible et de projectile, ainsi que la fonction d’onde du système composé. Les applications de cettethéorie sont présentées pour la réaction 14O(p,p’)14O, où le système composé 15F est un émetteurde proton, et pour la réaction 40Ca(d,d)40Ca

A 21st Century View of Nuclear Structure

Exploiting exact and special symmetries to unmask simplicity within complexity, which remains the “holy grail” of nuclear physics, will be considered within its historical context and as evolving through 21st century ab initio methods, including emerging results linked to the internal structure of nucleons. Some exemplar results for very light to medium mass nuclei will be presented, and what these may portend for heavier systems, including species beyond known lines of stability, will be proffered

A 21

Exploiting exact and special symmetries to unmask simplicity within complexity, which remains the “holy grail” of nuclear physics, will be considered within its historical context and as evolving through 21st century ab initio methods, including emerging results linked to the internal structure of nucleons. Some exemplar results for very light to medium mass nuclei will be presented, and what these may portend for heavier systems, including species beyond known lines of stability, will be proffered

White paper: from bound states to the continuum

International audienceThis white paper reports on the discussions of the 2018 Facility for Rare Isotope Beams Theory Alliance (FRIB-TA) topical program ‘From bound states to the continuum: Connecting bound state calculations with scattering and reaction theory’. One of the biggest and most important frontiers in nuclear theory today is to construct better and stronger bridges between bound state calculations and calculations in the continuum, especially scattering and reaction theory, as well as teasing out the influence of the continuum on states near threshold. This is particularly challenging as many-body structure calculations typically use a bound state basis, while reaction calculations more commonly utilize few-body continuum approaches. The many-body bound state and few-body continuum methods use different language and emphasize different properties. To build better foundations for these bridges, we present an overview of several bound state and continuum methods and, where possible, point to current and possible future connections