Nuclear Theory·nucl-th

Thursday·July 17, 2025

7 papers—5 primary·2 cross-listed

01
[Submitted on 15 Jul 2025]
Uncertainty band evaluation of optical potentials and differential cross-sections. Application to $^{8}$ Li + $^{58}$ Ni elastic scattering
O. C. B. Santos · J. Gómez-Camacho
A statistical method is presented to evaluate the uncertainty bands in the optical nucleus-nucleus potential and in differential cross sections. The starting point is the least square fit of a set of experimental values of elastic differential cross sections, varying the relevant optical potential parameters. This is done using standard $χ^{2}$ minimization codes, that provide the covariance matrix of the parameters. A maximum likelihood exploration of the $χ^{2}$ surface in parameter space allows to determine the covariance matrix of the parameters associated to a contour of a given $χ^{2}$ value. Bayes theorem allows to assign probabilities (p-values) to the regions in parameter space, characterized by $χ^{2}$ contours. The method allows to obtain uncertainty bands of an arbitrary observables associated to a given p-value using two approaches. The general approach determines the extremes of the observables calculated in the region of parameter space associated to that p-value. This requires an adequate sampling of parameter space, and explicit calculations of the observables on all sampling points. The simplified approach considers uncertainty propagation of the observable in terms of the optical model parameters. This involves the least-square covariance matrix, given by $χ^{2}$ minimization codes, and analytically calculated enhancement factors for each p-value. The method, in the general and simplified approaches, is applied to recent measurements of the elastic differential cross sections of $^{8}$ Li + $^{58}$ Ni. $1 σ$ and $2 σ$ uncertainty bands are obtained for the optical potentials as a function of the distance, and the differential cross sections as a function of the angle. The general and simplified approaches are very similar in this case. The application of the procedure to determine uncertainty bands of complex scattering calculations is discussed.
Comments:
20 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2507.11591 [pdf]
PRC(2026)·0 citations
02
[Submitted on 15 Jul 2025]
The $β$ -decay properties of $N = Z$ nuclei: Role of neutron-proton pairing and the shell model interpretation
Priyanka Choudhary · Chong Qi
We study the recently measured beta-decay of $^{70}$ Kr into $^{70}$ Br within the framework of the large-scale shell model. The enhancement in the Gamow-Teller (GT) transition strength in $^{70}$ Br compared to the $β$ -decay of the lighter $^{62}$ Ge was suggested as an indication for increased neutron-proton ( $n p$ ) pairing correlation. To explore the $n p$ correlations in nuclei, we systematically examined the $β$ -decay properties of the even-even nuclei $A = 58, 62, 66,$ and $70$ into $N = Z$ odd-odd nuclei. By employing an interaction involving solely $J = 1, T = 0$ and $J = 0, T = 1$ pairing matrix elements, we observe that the pairing does not necessarily lead to an enhancement in the GT strength for the same coupling strength. But with the inclusion of the $g_{9/2}$ orbital, the GT strength can be increased with increasing $n p$ pairing in connection with the enhanced contribution from the $g_{9/2}$ orbital. We further compare those results with realistic calculations in the $f p$ and $f_{5/2} p g_{9/2}$ model space to gauge the contribution from $f_{7/2}$ and $g_{9/2}$ orbitals in the GT strengths. With the JUN45 interaction, there is an increment for the yrast $1^{+}$ state for the decay of $^{70}$ Kr as compared to the decay of $^{62}$ Ge due to increased $g_{9/2}$ contribution. Additionally, we probe the effect of $n p$ pairing on $B_{GT}$ by modifying the single-particle energies and the $T = 0$ matrix elements of the interaction responsible for the decay transition strength. In calculations with realistic interaction, we find that the accumulated transition strength can increase with enhanced $n p$ pairing.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2507.11769 [pdf]
PRC(2025)·5 citations
03
[Submitted on 15 Jul 2025]
Monopole and Seniority Truncations in the Large-Scale Configuration Interaction Shell Model Approach
Priyanka Choudhary · Chong Qi
This paper addresses the challenges of solving the quantum many-body problem, particularly within nuclear physics, through the configuration interaction (CI) method. Large-scale shell model calculations often become computationally infeasible for systems with a large number of valence particles, requiring truncation techniques. We propose truncation methods for the nuclear shell model, in which angular momentum is conserved and rotational symmetry is restored. We introduce the monopole-interaction-based truncation and seniority truncation strategies, designed to reduce the dimension of the calculations. These truncations can be established by considering certain partitions based on their importance and selecting physically meaningful states. We examine these truncations for Sn, Xe, and Pb isotopes, demonstrating their effectiveness in overcoming computational limits. These truncations work well for systems with either a single type of valence nucleon or with both types. With these truncations, we are able to achieve good convergence for the energy at a very small portion of the total dimension.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2507.11796 [pdf]
Symmetry(2024)·2 citations
04
[Submitted on 16 Jul 2025]
Intrinsic spin distributions in multinucleon transfer reactions
Dan Dan Zhang · Dario Vretenar · Tamara Nikšić · Peng Wei Zhao · Jie Meng
Time-dependent covariant density functional theory (TD-CDFT) combined with angular momentum projection is developed and applied to study multinucleon transfer (MNT) reactions, with a focus on the intrinsic angular momentum distributions of the final fragments. Using the illustrative reaction $^{40}$ Ca + $^{208}$ Pb across a range of impact parameters, we find that the MNT process generates broad distributions of intrinsic spins. These distributions arise from the conversion of relative orbital angular momentum into intrinsic spin due to frictional interactions between the colliding nuclei. Additionally, mutual information (entanglement Shannon entropy) is employed to analyze correlations between the intrinsic spins of the fragments.
Comments:
13 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2507.11905 [pdf]
PLB(2025)·7 citations
05
[Submitted on 16 Jul 2025]
M1 dipole strength from projected generator coordinate method calculations in the sd-shell valence space
Stavros Bofos🇫🇷 · Jaime Martínez-Larraz🇪🇸 · Benjamin Bally🇩🇪 · Thomas Duguet🇫🇷 · Mikael Frosini🇫🇷 · Tomás R. Rodríguez🇪🇸 · Kamila Sieja🇫🇷
The low-energy enhancement observed in the deexcitation $γ$ -ray strength functions, attributed to magnetic dipole (M1) radiations, has spurred theoretical efforts to improve on its description. Among the most widely used approaches are the quasiparticle random-phase approximation (QRPA) and its extensions. However, these methods often struggle to reproduce the correct behavior of the M1 strength at the lowest $γ$ energies. An alternative framework, the projected generator coordinate method (PGCM), offers significant advantages over QRPA by restoring broken symmetries and incorporating both vibrational and rotational dynamics within a unified description. Due to these features, PGCM has been proposed as a promising tool to study the low-energy M1 strength function in atomic nuclei. However, comprehensive investigations employing this method are lacking. The PGCM is presently used within the frame of sd-shell valence space calculations based on the USDB shell-model interaction to benchmark its performance against the solutions obtained via exact diagonalization. The reliability of two different sets of generator coordinates in the PGCM calculations is gauged using $^{24}$ Mg as a test case. The ability of the PGCM to reproduce results from exact diagonalization in the sd valence space is demonstrated for $1^{+}$ states and M1 transitions. Future work will need to assess whether the proposed method can be applied systematically and extended to large-scale calculations while maintaining a reasonable computational cost.
Comments:
12 pages, 9 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2507.12037 [pdf]
PRC(2025)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE

Uncertainty band evaluation of optical potentials and differential cross-sections. Application to 8Li + 58Ni elastic scattering

The β-decay properties of N=Z nuclei: Role of neutron-proton pairing and the shell model interpretation

Monopole and Seniority Truncations in the Large-Scale Configuration Interaction Shell Model Approach

Intrinsic spin distributions in multinucleon transfer reactions

M1 dipole strength from projected generator coordinate method calculations in the sd-shell valence space

Affiliations

Uncertainty band evaluation of optical potentials and differential cross-sections. Application to $^{8}$ Li + $^{58}$ Ni elastic scattering

The $β$ -decay properties of $N = Z$ nuclei: Role of neutron-proton pairing and the shell model interpretation