Nuclear Theory·nucl-th

Wednesday·May 4, 2016

9 papers—6 primary·3 cross-listed

01
Nuclear response theory for spin-isospin excitations in a relativistic quasiparticle-phonon coupling framework
Caroline Robin🇺🇸 · Elena Litvinova🇺🇸
A new theoretical approach to spin-isospin excitations in open-shell nuclei is presented. The developed method is based on the relativistic meson-exchange nuclear Lagrangian of Quantum Hadrodynamics and extends the response theory for superfluid nuclear systems beyond relativistic quasiparticle random phase approximation in the proton-neutron channel (pn-RQRPA). The coupling between quasiparticle degrees of freedom and collective vibrations (phonons) introduces a time-dependent effective interaction, in addition to the exchange of pion and $ρ$ -meson taken into account without retardation. The time-dependent contributions are treated in the resonant time-blocking approximation, in analogy to previously developed relativistic quasiparticle time blocking approximation (RQTBA) in the neutral (non-isospin-flip) channel. The new method is called proton-neutron RQTBA (pn-RQTBA) and applied to Gamow-Teller resonance in a chain of neutron-rich Nickel isotopes $^{68 - 78}$ Ni. A strong fragmentation of the resonance along with quenching of the strength, as compared to pn-RQRPA, is obtained. Based on the calculated strength distribution, beta-decay half-lives of the considered isotopes are computed and compared to pn-RQRPA half-lives and to experimental data. It is shown that a considerable improvement of the half-life description is obtained in pn-RQTBA because of the spreading effects, which bring the lifetimes to a very good quantitative agreement with data.
nucl-thEPJA(2016)·59 citations
02
Beyond mean-field boson-fermion model for odd-mass nuclei
K. Nomura · T. Nikšić · D. Vretenar
A novel method for calculating spectroscopic properties of medium-mass and heavy atomic nuclei with an odd number of nucleons is introduced, based on the framework of nuclear energy density functional theory and the particle-core coupling scheme. The deformation energy surface of the even-even core, as well as the spherical single-particle energies and occupation probabilities of the odd particle(s), are obtained in a self-consistent mean-field calculation determined by the choice of the energy density functional and pairing interaction. This method uniquely determines the parameters of the Hamiltonian of the boson core, and only the strength of the particle-core coupling is specifically adjusted to selected data for a particular nucleus. The approach is illustrated in a systematic study of low-energy excitation spectra and transition rates of axially deformed odd-mass Eu isotopes.
nucl-thPRC(2016)·46 citations
03
Algebraic benchmark for prolate-oblate coexistence in nuclei
A. Leviatan · D. Shapira
We present a symmetry-based approach for prolate-oblate and spherical-prolate-oblate shape coexistence, in the framework of the interacting boson model of nuclei. The proposed Hamiltonian conserves the SU(3) and $SU (3)$ symmetry for the prolate and oblate ground bands and the U(5) symmetry for selected spherical states. Analytic expressions for quadrupole moments and $E 2$ rates involving these states are derived and isomeric states are identified by means of selection rules.
nucl-thnucl-exquant-phPRC(2016)·23 citations
04
Microscopic analysis of p^{10}B scattering at the intermediate energies
Albert Dzhazairov-Kahramanov · Elena Ibraeva · Pavel Krassovitskiy
The differential cross sections of the p^{10}B scattering at energies of 197, 600 and 1000 MeV have been calculated within the framework of the Glauber theory. The operator of multiple scattering takes into account the contributions of single and double collisions. The contributions from protons scattering on the nucleons of different shells have been estimated in the single-scattering cross-section. The comparison with the experiment at 197 MeV and with DWBA calculation showed the adequate description of cross-sections in the region of the front angles.
nucl-th0 citations
05
Multidimensionally-constrained covariant density functional theories --- nuclear shapes and potential energy surfaces
Shan-Gui Zhou
The intrinsic nuclear shapes deviating from a sphere not only manifest themselves in nuclear collective states but also play important roles in determining nuclear potential energy surfaces (PES's) and fission barriers. In order to describe microscopically and self-consistently nuclear shapes and PES's with as many shape degrees of freedom as possible included, we developed multidimensionally-constrained covariant density functional theories (MDC-CDFTs). In MDC-CDFTs, the axial symmetry and the reflection symmetry are both broken and all deformations characterized by $β_{λ μ}$ with even $μ$ are considered. We have used the MDC-CDFTs to study PES's and fission barriers of actinides, the non-axial octupole $Y_{32}$ correlations in $N = 150$ isotones and shapes of hypernuclei. In this Review we will give briefly the formalism of MDC-CDFTs and present the applications to normal nuclei.
nucl-thnucl-exPhys.Scripta(2016)·133 citations
06
Transition from direct to sequential two-proton decay in $s$ - $d$ shell nuclei
T.A. Golubkova · X. Xu · L.V. Grigorenko · I.G. Mukha · C. Scheidenberger · M.V. Zhukov
Transitions among different mechanisms of two-proton decay are studied in general. The introduced improved direct-decay model generalizes the semi-analytical models used before and provides flawless phenomenological description of three-body correlations in $2 p$ decays. This is demonstrated by examples of the low-lying $^{16}$ Ne state decays. Different forms of transition dynamic are shown to be highly probable beyond the proton dripline for the $s$ - $d$ shell nuclei. It is demonstrated that transition dynamic of $2 p$ emitters can provide means for extraction of a width of the ground-state resonance of a core+ $p$ subsystem of the core+ $2 p$ system. Practical applicability of the method is demonstrated by properties of the $^{14}$ F ground state derived from the $^{15} \mbox N e \to^{13} \mbox O + 2 p$ decay data and of the $^{29}$ Cl ground state derived from the $^{30} \mbox A r \to^{28} \mbox S + 2 p$ decay data.
nucl-thPLB(2016)·17 citations
07
Aspects of the momentum dependence of the equation of state and of the residual $N N$ cross section, and their effects on nuclear stopping
Z. Basrak🇭🇷 · P. Eudes🇫🇷 · V. de la Mota🇫🇷
With the semiclassical Landau-Vlasov transport model we studied the stopping observable $R_{E}$ , the energy-based isotropy ratio, for the $^{129}$ Xe\,+\, $^{120}$ Sn reaction at beam energies spanning 12 $A$ to 100 $A$ MeV. We investigated the impacts of the nonlocality of the nuclear mean field, of the in-medium modified nucleon-nucleon ( $N N$ ) cross section and of the reaction centrality. A fixed set of model parameters yields $R_{E}$ values that favorably compare with the experimental ones, but only for energies below the Fermi energy $E_{F}$ . Above $E_{F}$ agreement is readily possible, but by a smooth evolution with energy of the parameter that controls the in-medium modification of $N N$ cross section. By comparing the simulation correction factor $F$ applied to the free $N N$ cross section with the one deduced from experimental data [Phys.\ Rev.\ C\,{\bf 90}, 064602 (2014)], we infer that the zero-range mean field almost entirely reproduces it. Also, in accordance with what has been deduced from experimental data, around $E_{F}$ a strong reduction of the free $N N$ cross section is found. In order to test the impact of sampling central collisions by multiplicity an event generator (HIPSE) was used. We obtain that high multiplicity events are spread over a broad impact parameter range, but it turns out that this has a small effect on the observable $R_{E}$ and, thus, on $F$ as well.
↳ nucl-exnucl-thPRC(2016)·23 citations
08
Spectral functions and in-medium properties of hadrons
Ralf-Arno Tripolt🇮🇹 · Lorenz von Smekal🇩🇪 · Jochen Wambach🇮🇹
The in-medium modifications of hadron properties such as masses and decay widths have been a major focus of the scientific work of Gerry Brown and the insights gained by him and his collaborators made them major drivers of this field for several decades. Their prediction of experimental signals in di-lepton pair production in relativistic heavy-ion collisions were instrumental in initiating large experimental campaigns which continue until today. In this chapter we review recent results which elucidate the relation of hadronic spectral properties at finite temperature and density to the restoration of spontaneously broken chiral symmetry.
↳ hep-phhep-thnucl-thIJMPE(2017)·22 citations
09
Transverse pion structure beyond leading twist in constituent models
C. Lorcé (Ecole Polytechnique, CPHT)🇫🇷 · B. Pasquini (Pavia U. & INFN, Pavia)🇮🇹 · P. Schweitzer (Connecticut U. and Tubingen U.)🇩🇪
The understanding of the pion structure as described in terms of transverse-momentum dependent parton distribution functions (TMDs) is of importance for the interpretation of currently ongoing Drell-Yan experiments with pion beams. In this work we discuss the description of pion TMDs beyond leading twist in a pion model formulated in the light-front constituent framework. For comparison, we also review and derive new results for pion TMDs in the bag and spectator models.
↳ hep-phhep-exnucl-exnucl-thEPJC(2016)·48 citations

Affiliations

first authorsco-authorsvia INSPIRE