Nuclear Theory·nucl-th

Friday·December 29, 2017

13 papers—10 primary·3 cross-listed

01
Beyond the 2-Body Interaction Paradigm: The Case for Extended A-Body Pairing Interaction in Nuclei
V.G. Gueorguiev
We discuss modeling of nuclear structure beyond the 2-body interaction paradigm. Our first example is related to the need of three nucleon contact interaction terms suggested by chiral perturbation theory. The relationship of the two low-energy effective coupling parameters for the relevant three nucleon contact interaction terms $c_{D}$ and $c_{E}$ that reproduce the binding energy of $^{3}$ H and $^{3}$ He has been emphasized and the physically relevant parameter region has been illustrated using the binding energy of $^{4}$ He. Further justification of A-body interaction terms is outlined based on the Okubo-Lee-Suzuki effective interaction method used in solving the nuclear many-body problem within a finite model space. The third example we use is an exactly solvable A-body extended pairing interaction applied to heavy nuclei with a long isotopic chains, in particular using $^{132}$ Sn and $^{208}$ Pb as closed core system illustrates a remarkable relationship between the extended pairing strength $G (A)$ and the size of the valence space $dim (A)$ for the members of these two isotope chain: $G (A) = α dim (A)^{- β}$ with $α = 259.436$ for Sn and $α = 366.77$ for Pb while the parameter $β$ is practically 1. These three cases present evidence for the need of better understanding of the three-nucleon (NNN), four-nucleon (NNNN), and A-body interactions in nuclei either derived from ChPT or from a phenomenological considerations.
nucl-thNucl.Theor.(2017)·0 citations
02
Microscopic description of fission in odd-mass uranium and plutonium nuclei with the Gogny energy density functional
R. Rodríguez-Guzmán · L.M. Robledo
The parametrization D1M of the Gogny energy density functional is used to study fission in the odd-mass Uranium and Plutonium isotopes with A=233,\ldots,249 within the framework of the Hartree-Fock-Bogoliubov (HFB) Equal Filling Approximation (EFA). Ground state quantum numbers and deformations, pairing energies, one-neutron separation energies, barrier heights and fission isomer excitation energies are given. Fission paths, collective masses and zero point rotational and vibrational quantum corrections are used to compute the systematic of the spontaneous fission half-lives t $_{S F}$ , the masses and charges of the fission fragments as well as their intrinsic shapes. Although there exits a strong variance of the predicted fission rates with respect to the details involved in their computation, it is shown that both the specialization energy and the pairing quenching effects, taken into account fully variationally within the HFB-EFA blocking scheme, lead to larger spontaneous fission half-lives in odd-mass U and Pu nuclei as compared with the corresponding even-even neighbors. It is shown that modifications of a few percent in the strengths of the neutron and proton pairing fields can have a significant impact on the collective masses leading to uncertainties of several orders of magnitude in the predicted t $_{S F}$ values. Alpha-decay lifetimes have also been computed using a parametrization of the Viola-Seaborg formula.
nucl-thEPJA(2017)·26 citations
03
Kaonic deuterium and low-energy antikaon-nucleon interaction
Wataru Horiuchi🇯🇵 · Tetsuo Hyodo🇯🇵 · Wolfram Weise🇩🇪
A new evaluation of the $1 s$ level shift and width of kaonic deuterium is presented based on an accurate $K ˉ N N$ three-body calculation, using as input a realistic antikaon-nucleon interaction constrained by the SIDDHARTA kaonic hydrogen data. The three-body Schrödinger equation is solved with a superposition of a large number of correlated Gaussian basis functions extending over distance scales up to several hundred fm. The resulting energy shift and width of the kaonic deuterium $1 s$ level are $E ≃ 0.67$ keV and $Γ ≃ 1.02$ keV, with estimated uncertainties at the 10% level.
nucl-thEPJ Web Conf.(2018)·2 citations
04
Manifestation of {\alpha}-clustering in $^{10}$ Be via {\alpha}-knockout reaction
Mengjiao Lyu · Kazuki Yoshida · Yoshiko Kanada-En'yo · Kazuyuki Ogata
Background: Proton-induced {\alpha}-knockout reactions empower direct experimental manifestations of {\alpha}-clustering in nuclei. This is obtained by relating the theoretical descriptions of clustering states with experimental reaction observables. It is desired to introduce microscopic structure models into the theoretical frameworks for {\alpha}-knockout reactions. Purpose: Our goal is to probe the {\alpha}-clustering in $^{10}$ Be nucleus by proton-induced {\alpha}-knockout reaction observables. Method: We adopt an extended version of the Tohsaki-Horiuchi-Schuck-Röpke (THSR) wave function of $^{10}$ Be and integrate it with the distorted wave impulse approximation (DWIA) framework for the calculation of (p,p{\alpha}) knockout reactions. Results: We make the first calculation for the $^{10}$ Be(p,p{\alpha}) $^{6}$ He reaction at 250 MeV implementing a microscopic {\alpha}-cluster wave function and predict the triple differential cross sections (TDX). Furthermore, by constructing artificial states of the target nucleus $^{10}$ Be with compact or dilute spatial distributions, the TDX is found to be highly sensitive to the extent of clustering in the target nuclei. Conclusions: These results provide reliable manifestation of the {\alpha}-clustering in $^{10}$ Be.
nucl-thPRC(2018)·29 citations
05
Competition between magnetic catalysis effect and chiral rotation effect
Lingxiao Wang🇨🇳 · Gaoqing Cao🇨🇳
In this work, we explore the competition between magnetic catalysis effect and chiral rotation effect in a general parallel electromagnetic field within the effective Nambu--Jona-Lasinio model. For a given electric field $E$ at zero temperature, the mass gap shows three different features with respect to an increasing magnetic field $B$ : increasing monotonically, decreasing after increasing and decreasing monotonically. By making use of strong magnetic field approximation, we illuminate that this is due to the competition between catalysis effect and chiral rotation effect induced both by the magnetic field, and a critical electric field $e E_{c} = 86.4 MeV$ is found beyond which the mass gap will eventually decrease at large $B$ . As only large magnetic field is relevant for the derivation, the critical electric field does not depend on the temperature $T$ or chemical potential $μ$ .
nucl-thPRD(2018)·14 citations
06
Isospin dynamics in nuclear structure
Elena Litvinova🇺🇸 · Caroline Robin🇺🇸 · Peter Schuck🇫🇷
We discuss some special aspects of the nuclear many-body problem related to isospin transfer. The major quantity of interest is the in-medium propagator of a particle-hole configuration of the proton-neutron character, which determines the nuclear response to isospin transferring external fields. One of the most studied excitation modes is the Gamow-Teller resonance (GTR), which can, therefore, be used as a sensitive test for the theoretical approaches. Its low-energy part, which is responsible for the beta decay half-lives, is especially convenient for this. Models benchmarked against the GTR can be used to predict other, more exotic, excitations studied at nuclear rare isotope beam facilities and in astrophysics. As far as the precision is concerned, the major problem in such an analysis is to disentangle the effects related to the underlying interaction and those caused by the many-body correlations. Therefore, approaches (i) based on fundamental concepts for the nucleon-nucleon interaction which (ii) include complex many-body dynamics are the preferred ones. We discuss progress and obstacles on the way to such approaches.
nucl-thEPJ Web Conf.(2018)·1 citation
07
Impact parameter smearing effects on isospin sensitive observables in heavy ion collisions
Li Li · Yingxun Zhang · Zhuxia Li · Nan Wang · Ying Cui · Jack Winkelbauer
The validity of impact parameter estimation from the multiplicity of charged particles at low-intermediate energies is checked within the framework of ImQMD model. The simulations show that the multiplicity of charged particles cannot estimate the impact parameter of heavy ion collisions very well, especially for central collisions at the beam energies lower than $\sim$ 70 MeV/u due to the large fluctuations of the multiplicity of charged particles. The simulation results for the central collisions defined by the charged particle multiplicity are compared to those by using impact parameter b=2 fm and it shows that the charge distribution for $^{112}$ Sn + $^{112}$ Sn at 50 MeV/u is different evidently for two cases; and the chosen isospin sensitive observable, the coalescence invariant single neutron to proton yield ratio, reduces less than 15\% for neutron-rich systems $^{124, 132}$ Sn + $^{124}$ Sn at $E_{b e am}$ =50 MeV/u, while the coalescence invariant double neutron to proton yield ratio does not have obvious difference. The sensitivity of the chosen isospin sensitive observables to effective mass splitting is studied for central collisions defined by the multiplicity of charged particles. Our results show that the sensitivity is enhanced for $^{132}$ Sn+ $^{124}$ Sn relative to that for $^{124}$ Sn+ $^{124}$ Sn, and this reaction system should be measured in future experiments to study the effective mass splitting by heavy ion collisions.
nucl-thnucl-exPRC(2018)·19 citations
08
Large-scale exact diagonalizations reveal low-momentum scales of nuclei
C. Forssén · B. D. Carlsson · H. T. Johansson · D. Sääf · A. Bansal · G. Hagen · T. Papenbrock
Ab initio methods aim to solve the nuclear many-body problem with controlled approximations. Virtually exact numerical solutions for realistic interactions can only be obtained for certain special cases such as few-nucleon systems. Here we extend the reach of exact diagonalization methods to handle model spaces with dimension exceeding $1 0^{10}$ on a single compute node. This allows us to perform no-core shell model (NCSM) calculations for 6Li in model spaces up to $N_{max} = 22$ and to reveal the 4He+d halo structure of this nucleus. Still, the use of a finite harmonic-oscillator basis implies truncations in both infrared (IR) and ultraviolet (UV) length scales. These truncations impose finite-size corrections on observables computed in this basis. We perform IR extrapolations of energies and radii computed in the NCSM and with the coupled-cluster method at several fixed UV cutoffs. It is shown that this strategy enables information gain also from data that is not fully UV converged. IR extrapolations improve the accuracy of relevant bound-state observables for a range of UV cutoffs, thus making them profitable tools. We relate the momentum scale that governs the exponential IR convergence to the threshold energy for the first open decay channel. Using large-scale NCSM calculations we numerically verify this small-momentum scale of finite nuclei.
nucl-thPRC(2018)·44 citations
09
Evolution of single-particle structure of silicon isotopes
O. Bespalova · N. Fedorov · A. Klimochkina · M. Markova · T. Spasskaya · T. Tretyakova
New data on proton and neutron single-particle energies $E_{n l j}$ of Si isotopes with neutron number $N$ from 12 to 28 as well as occupation probabilities $N_{n l j}$ of single particle states of stable isotopes $^{28, 30}$ Si near the Fermi energy were obtained by the joint evaluation of the stripping and pick-up reaction data and excited state decay schemes of neighboring nuclei. The evaluated data indicate following features of single-particle structure evolution: persistence of $Z = 14$ subshell closure with $N$ increase, the new magicity of the number $N = 16$ , and the conservation of the magic properties of the number $N = 20$ in Si isotopic chain. The features were described by the dispersive optical model. The calculation also predicts the weakening of $N = 28$ shell closure and demonstrates evolution of bubble-like structure of the proton density distributions in neutron-rich Si isotopes.
nucl-thnucl-exEPJA(2018)·10 citations
10
Low-Energy Effective Field Theory of Lepton-Proton Bremsstrahlung
P. Talukdar🇮🇳 · F. Myhrer🇺🇸 · U. Raha🇮🇳
We calculate the cross section for the lepton-proton bremsstrahlung process $l + p \to l^{'} + p + γ$ in effective field theory. This process corresponds to an undetected background signal for the proposed MUSE experiment at PSI. MUSE is designed to measure elastic scattering of low-energy electrons and muons off a proton target in order to extract a precise value for the proton's r.m.s. radius. We show that the commonly used {\it peaking approximation}, which is used to evaluate the {\it radiative tail} for the elastic cross section, is not applicable for muon proton scattering at the low-energy MUSE kinematics. We also correct a misprint in a commonly cited review article.
nucl-thhep-ph5 citations

Affiliations

first authorsco-authorsvia INSPIRE