Bulletin of the American Physical Society
2020 Fall Meeting of the APS Division of Nuclear Physics
Volume 65, Number 12
Thursday–Sunday, October 29–November 1 2020; Time Zone: Central Time, USA
Session RM: Nuclear Theory III: Structure and Reactions |
Hide Abstracts |
Chair: Kevin Fossez, Argonne National Laboratory |
Sunday, November 1, 2020 8:30AM - 8:42AM |
RM.00001: $R$-Matrix Approaches to Isospin and Mirror Symmetry Carl Brune $R$-matrix theory may utilized to relate partial widths or asymptotic normalization constants in one nucleus to the corresponding quantities for states in other nuclei that are related by isospin or mirror symmetry. Specific methods of implementing these relationships will be reviewed and applied to $s$-wave mirror levels in nucleon+${}^{12}{\rm C}$, nucleon+${}^{16}{\rm O}$, and nucleon+${}^{26}{\rm Al}$. Particular attention is paid to effects arising from beyond the nuclear surface, where isospin symmetry is strongly violated. Finally, a new approach to multi-level mirror symmetry is derived and applied to the first three $2^+$ states of ${}^{18}{\rm O}$ and ${}^{18}{\rm Ne}$. In this case, significant deviations from naive mirror symmetry are found, due to external mixing of the levels. [Preview Abstract] |
Sunday, November 1, 2020 8:42AM - 8:54AM |
RM.00002: Global performance and optimization of separable pairing in covariant density functional theory Saja Teeti, Anatoli Afanasjev Over the recent years separable pairing interaction [1] has found a widespread use in covariant density functional theory (CDFT) as an alternative to the pairing interaction based on the finite range Gogny force [2]. Both types of pairing allow to eliminate the uncertainties connected with the definition of the size of pairing window, but the former one is less numerically time-consuming. For the first time we carried out the global analysis of the performance of separable pairing and its optimization as a function of mass, proton and neutron numbers. The analysis is based on the comparison of calculated $\Delta_{uv}$ pairing gaps in even-even nuclei [which according to Ref. [4] represents the best measure of pairing correlations] with experimental $\Delta^{(5)}$ pairing indicators. The impact of time-odd mean fields on pairing indicators is taken into account. [1] Y. Tian, Z. Y. Ma, and P. Ring, Phys. Lett. B 676, 44 (2009). [2] D. Vretenar, A.V. Afanasjev, G.A. Lalazissis and P. Ring, Phys. Rep. 409 (2005) 101. [3] S. Teeti and A. V. Afanasjev, in preparation. [4] S. E. Agbemava, A. V. Afanasjev, D. Ray, and P. Ring, Phys. Rev. C 89, 054320 (2014). [Preview Abstract] |
Sunday, November 1, 2020 8:54AM - 9:06AM |
RM.00003: Examining isospin-mixing in the $sd$ shell using new isospin-breaking ``USD'' Hamiltonians Aaron Magilligan, B. Alex Brown Two new USD-type Hamiltonians, USDC and USDI, have been developed [1] that directly incorporate Coulomb and other isospin-breaking interactions. Starting from ab initio interactions, linear combinations of two-body matrix elements were constrained by experimental energy levels in \textit{sd}-shell nuclei. With this method, binding energies and excitation energies of proton-rich nuclei in the shell can be added to the data set used in the fit. USDC is based on the same renormalized G matrix used in the derivation of previous USD-type Hamiltonians, while USDI is derived from in-medium similarity renormalization group (IMSRG) interactions. Both contain an analytic Coulomb interaction with Miller-Spencer short-range correlations and an effective isotensor interaction. These Hamiltonians are used to examine isospin-level mixing, Thomas-Ehrman shifts, and other properties of \textit{sd}-shell nuclei. \\ \noindent [1] A. Magilligan and B. A. Brown, Phys. Rev. C \textbf{101}, 064312 (2020) [Preview Abstract] |
Sunday, November 1, 2020 9:06AM - 9:18AM |
RM.00004: Basis truncation schemes in the symplectic no-core configuration interaction framework Jakub Herko, Mark Caprio, Patrick Fasano, Anna McCoy, Tomas Dytrych, Pieter Maris The no-core configuration interaction (NCCI) framework is an \textit{ab initio} method predicting properties of light nuclei from the underlying internucleon interaction. However, the dimension of the NCCI model space rapidly increases with the maximal number of allowed excitation oscillator quanta and the number of nucleons, which limits the convergence of calculated observables that can be achieved in practice. To obtain more converged results we can make use of the approximate Sp(3,R) symplectic symmetry of the nuclear many-body problem by working in a basis organized according to this symmetry and truncating the basis in a scheme capturing the most important nuclear degrees of freedom. In the symplectic NCCI (SpNCCI) framework, we carry out calculations in a center-of-mass free basis organized according to the Sp(3,R) symmetry. We present different basis truncation schemes and their effect on the dimension of the SpNCCI model space. [Preview Abstract] |
Sunday, November 1, 2020 9:18AM - 9:30AM |
RM.00005: Benchmarking projected Hartree-Fock as an approximation Stephanie Lauber, Calvin Johnson, Hayden Frye We benchmark angular-momentum projected Hartree-Fock calculations as an approximation to full configuration-interaction results in a shell model basis. For such a simple approximation we find reasonably good agreement between excitation spectra, including for add-A and odd-odd nuclei. Key to this, we argue, is the use of gradient descent. We also find cases where shape-coexistence demonstrably improves the spectrum and make an application to Ge even-even nuclei. [Preview Abstract] |
Sunday, November 1, 2020 9:30AM - 9:42AM |
RM.00006: Level densities and $\gamma$-ray strength functions of heavy nuclei in the static-path plus random-phase approximation Paul Fanto, Yoram Alhassid We apply the static-path plus random-phase approximation (SPA+RPA) to calculate nuclear level densities and $\gamma$-ray strength functions ($\gamma$SFs), which are important inputs to statistical models of compound-nucleus reactions. Formulated in the configuration-interaction (CI) shell model framework, the SPA+RPA includes static fluctuations beyond the mean field and small-amplitude time-dependent quantal fluctuations. Using effective interactions that include pairing plus multipole-multipole terms, we calculate state densities of $^{148-155}$Sm in the SPA+RPA and find them to be in excellent agreement with exact densities obtained with the shell-model Monte Carlo (SMMC) method. We compare the SPA+RPA densities to mean-field densities and find that the SPA+RPA repairs deficiencies of the mean-field approximation associated with broken symmetries. In particular, we reproduce the rotational enhancement in deformed nuclei, and resolve the problem of the unphysical negative entropy associated with the pairing condensate. Using a quadrupole-quadrupole interaction in $sd$-shell nuclei, we also find that the SPA+RPA $E2$ and $M1$ $\gamma$SFs reproduce the qualitative features of the exact CI shell model $\gamma$SFs. We provide an outlook for applications to lanthanide nuclei. [Preview Abstract] |
Sunday, November 1, 2020 9:42AM - 9:54AM |
RM.00007: The Emergence of Collectivity in Heavy Nuclei in the Shell Model Monte Carlo Method Sohan Vartak, Yoram Alhassid, Marco Bonett-Matiz Understanding the microscopic origin of collectivity in heavy nuclei has been a long-standing problem in nuclear physics. The configuration-interaction (CI) shell model is one of the basic models for describing the structure of nuclei but its application to heavy nuclei has been severely limited because of the combinatorial increase of the dimensionality of the many-particle model space with the number of valence orbitals and/or number of nucleons. The shell model Monte Carlo (SMMC) method has addressed this problem by enabling calculations in model spaces that are many orders of magnitude larger than those that can be solved by conventional diagonalization techniques. However, SMMC has been mostly limited to the calculation of thermal and ground-state observables, and it has been a challenge to extract spectroscopic information on individual excited states. A method was recently developed to extract a few low-lying excited states for each spin and parity by SMMC calculations of one-body density response matrices in imaginary time [1]. We apply this method to chains of lanthanide isotopes and identify signatures of the crossover from vibrational to rotational collectivity in the spectra of these isotopes.\\$[1]$ Y. Alhassid, M. Bonett-Matiz and C.N. Gilbreth, to be published. [Preview Abstract] |
Sunday, November 1, 2020 9:54AM - 10:06AM |
RM.00008: Rotation in near and beyond proton and neutron drip line nuclei Anatoli Afanasjev, Saja Teeti, Ahmad Taninah, Naoyuki Itagaki Two new mechanisms active in rotating nuclei located in the vicinity of neutron and proton drip lines have been discovered [1,2]. Strong Coriolis interaction acting on high-j orbitals transforms particle-unbound (resonance) nucleonic configurations into particle-bound ones with increasing angular momentum. The point of the transition manifests the birth of particle-bound rotational bands. Alternative possibility of the transition from particle-bound to resonance rotational band (the death of particle-bound rotational bands) with increasing spin also exists but it is less frequent in the calculations. The birth of particle-bound rotational bands provides a mechanism for the extension of nuclear landscape beyond its boundaries in non-rotating nuclei. The mapping of nuclear landscape boundaries in rotating nuclei and systematic search of best candidates for experimental observation of these two phenomena are in progress [3]. Their results will be presented. [1] A.V.Afanasjev, N.Itagaki and D.Ray, Phys.Lett. B 794 (2019) 7. [2] A.V.Afanasjev, S.E.Agbemava and A.Taninah, Acta Physica Polonica, in press [3] S. Teeti, A. Taninah and A.V.Afanasjev, in preparation [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700