Showing papers by "Jie Meng published in 2020"

Deformed relativistic Hartree-Bogoliubov theory in continuum with a point-coupling functional: Examples of even-even Nd isotopes

Abstract: Background: The study of exotic nuclei far from the β stability line is stimulated by the development of radioactive ion beam facilities worldwide and brings opportunities and challenges to existing nuclear theories. Including self-consistently the nuclear superfluidity, deformation, and continuum effects, the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) has turned out to be successful in describing both stable and exotic nuclei. Due to several challenges, however, the DRHBc theory has only been applied to study light nuclei so far. Purpose: The aim of this work is to develop the DRHBc theory based on the point-coupling density functional and examine its possible application for all even-even nuclei in the nuclear chart by taking Nd isotopes as examples. Method: The nuclear superfluidity is taken into account via Bogoliubov transformation. Densities and potentials are expanded in terms of Legendre polynomials to include the axial deformation degrees of freedom. Sophisticated relativistic Hartree-Bogoliubov equations in coordinate space are solved in a Dirac Woods-Saxon basis to consider the continuum effects. Results: Numerical convergence for energy cutoff, angular momentum cutoff, Legendre expansion, pairing strength, and (un)constrained calculations are confirmed for the DRHBc theory from light nuclei to heavy nuclei. The ground-state properties of even-even Nd isotopes are calculated with the successful density functional PC-PK1 and compared with the spherical nuclear mass table based on the relativistic continuum Hartree-Bogoliubov (RCHB) theory as well as the available data. The calculated binding energies are in very good agreement with the existing experimental values with a rms deviation of 0.958MeV, which is remarkably smaller than 8.301MeV in the spherical case. The predicted proton and neutron drip-line nuclei for Nd isotopes are respectively Nd120 and Nd214, in contrast with Nd126 and Nd228 in the RCHB theory. The experimental quadrupole deformations and charge radii are reproduced well. An interesting decoupling between the oblate shape β2=−0.273 contributed by bound states and the nearly spherical one β2=0.047 contributed by continuum is found in Nd214. Contributions of different single-particle states to the total neutron density are investigated and an exotic neutron skin phenomenon is suggested for Nd214. The proton radioactivity beyond the proton drip line is discussed and Nd114, Nd116, and Nd118 are predicted to be candidates for two-proton or even multiproton radioactivity. Conclusions: The DRHBc theory based on the point-coupling density functional is developed and detailed numerical checks are performed. The techniques to construct the DRHBc mass table for even-even nuclei are explored and extended for all even-even nuclei in the nuclear chart by taking Nd isotopes as examples. The available experimental data are reproduced well. The deformation and continuum effects on drip-line nuclei, exotic neutron skin, and proton radioactivity are presented.

Symmetry energy at supra-saturation densities via the gravitational waves from GW170817

Abstract: Motivated by the historical detection of gravitational waves from GW170817, the neutron star and the neutron drop, i.e., a certain number of neutrons confined in an external field, are systematically investigated by ab initio calculations as well as the nonrelativistic and relativistic state-of-the-art density functional theories. Strong correlations are found among the neutron star tidal deformability, the neutron star radius, the root-mean-square radii of neutron drops, and the symmetry energies of nuclear matter at supra-saturation densities. For dense matter composed of nucleons only, these correlations, together with the upper limit on the tidal deformability extracted from GW170817, provides the constraints for the neutron star radii, the neutron drop radii, and the symmetry energy at twice saturation density as ${R}_{1.4\phantom{\rule{0.16em}{0ex}}{M}_{\ensuremath{\bigodot}}}\ensuremath{\leqslant}13.4\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{0.28em}{0ex}}\mathrm{km},\phantom{\rule{0.28em}{0ex}}{R}_{\mathrm{nd}}\ensuremath{\leqslant}2.41\ifmmode\pm\else\textpm\fi{}0.10\phantom{\rule{0.28em}{0ex}}\mathrm{fm}$, and ${E}_{\mathrm{sym}}(2{\ensuremath{\rho}}_{0})\ensuremath{\leqslant}60.7\ifmmode\pm\else\textpm\fi{}10.9\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$, respectively.

Selection rules of electromagnetic transitions for chirality-parity violation in atomic nuclei

Abstract: The nuclear Chirality-Parity (ChP) violation, a simultaneous breaking of chiral and reflection symmetries in the intrinsic frame, is investigated with a reflection-asymmetric triaxial particle rotor model. A new symmetry for an ideal ChP violation system is found and the corresponding selection rules of the electromagnetic transitions are derived. The fingerprints for the ChP violation including the nearly degenerate quartet bands and the selection rules of the electromagnetic transitions are provided. These fingerprints are examined for ChP quartet bands by taking a two-j shell h 11 / 2 and d 5 / 2 with typical energy spacing for A = 130 nuclei.

Selection rules of electromagnetic transitions for chirality-parity violation in atomic nuclei

Abstract: The nuclear Chirality-Parity (ChP) violation, a simultaneous breaking of chiral and reflection symmetries in the intrinsic frame, is investigated with a reflection-asymmetric triaxial particle rotor model A new symmetry for an ideal ChP violation system is found and the corresponding selection rules of the electromagnetic transitions are derived The fingerprints for the ChP violation including the nearly degenerate quartet bands and the selection rules of the electromagnetic transitions are provided These fingerprints are examined for ChP quartet bands by taking a two-$j$ shell $h_{11/2}$ and $d_{5/2}$ with typical energy spacing for $A=$ 130 nuclei

Impact of tensor forces on spin-orbit splittings in neutron-proton drops

Abstract: A systematic study of the tensor-force impact in neutron-proton drops has been reported using the relativistic Hartree-Fock (RHF) theory with the $\ensuremath{\pi}\text{\ensuremath{-}}N$ coupling strength optimized to the relativistic Brueckner-Hartree-Fock (RBHF) results for neutron drops. The evolutions of the neutron spin-orbit splittings as a function of the neutron number for neutron-proton drops with one proton behave similarly to the pure neutron drops, which show the tensor-force effect. By adding one more proton or neutron in the neutron drop with $N=20$, it is found that the tensor-force effect is more prominent between neutrons and protons than between neutrons. This can be attributed to the isospin factor in the tensor term of the $\ensuremath{\pi}\text{\ensuremath{-}}N$ interaction in the RHF density functional theory, which reflects the fact that the neutron-proton tensor force is stronger than the neutron-neutron one. Similar behavior for the spin-orbit splitting evolutions has also been found for the neutron-proton drops with 20 protons, where the tensor-force strength $\ensuremath{\lambda}$ is redetermined according to the RBHF results due to the large central densities of the systems.

Time-dependent covariant density functional theory in three-dimensional lattice space: Benchmark calculation for the O 16 + O 16 reaction

Abstract: Time-dependent covariant density functional theory with the density functional PC-PK1 is developed in a three-dimensional coordinate space without any symmetry restrictions, and benchmark calculations for the $^{16}\mathrm{O}+^{16}\mathrm{O}$ reaction are performed systematically. The relativistic kinematics, the conservation laws of the momentum, total energy, and particle number, as well as the time-reversal invariance are examined and confirmed to be satisfied numerically. Two primary applications including the dissipation dynamics and above-barrier fusion cross sections are illustrated. The obtained results are in good agreement with the ones given by the nonrelativistic time-dependent density functional theory and the data available. This demonstrates that the newly developed time-dependent covariant density functional theory could serve as an effective approach for the future studies of nuclear dynamical processes.

Pseudospin symmetry and octupole correlations for multiple chiral doublets in Ba 131

Abstract: A reflection-asymmetric triaxial particle rotor model with three quasiparticles and a reflection-asymmetric triaxial rotor is developed, and applied to investigate the observed multiple chiral doublets $(\mathrm{M}\ensuremath{\chi}\mathrm{D})$ candidates with octupole correlations in $^{131}\mathrm{Ba}$, i.e., two pairs of positive-parity bands D3-D4 and D5-D6, as well as one pair of negative-parity bands D7-D8. The energy spectra, the energy staggering parameters, the $B(M1)/B(E2)$ ratios, and the $B(E1)/B(E2)$ ratios are reproduced well. The chiral geometries for these $\mathrm{M}\ensuremath{\chi}\mathrm{D}$ candidates are examined by the azimuthal plots, and the evolution of chiral geometry with spin is clearly demonstrated. The intrinsic structure for the positive-parity bands is analyzed and the possible pseudospin-chiral quartet bands are suggested.

Quadrupole and octupole collectivity in $^{143}$Ba

Abstract: Author(s): Morse, C; MacChiavelli, AO; Crawford, HL; Zhu, S; Wu, CY; Wang, YY; Meng, J; Back, BB; Bucher, B; Campbell, CM; Carpenter, MP; Chen, J; Clark, RM; Cromaz, M; Fallon, P; Henderson, J; Janssens, RVF; Jones, MD; Khoo, TL; Kondev, FG; Lauritsen, T; Lee, IY; Li, J; Potterveld, D; Santamaria, C; Savard, G; Seweryniak, D; Stolze, S; Weisshaar, D | Abstract: The neutron-rich barium nuclei have been the subject of intense interest due to the enhanced octupole correlations they are predicted to exhibit. The observation of enhanced octupole collectivity in Ba144,146 as measured in sub-barrier Coulomb excitation, consistent with static octupole deformation, has further heightened this interest. In the present work, these studies are extended to the neighboring odd-mass Ba143 to investigate the interplay between single-particle and collective octupole degrees of freedom. A new measurement of the first 92 - state lifetime is also presented. Reflection-Asymmetric Triaxial Particle Rotor Model calculations indicate that the negative-parity bands in Ba143 can be understood as a decoupled structure of νh9/2 parentage, while the positive-parity bands are built on a decoupled octupole phonon. No evidence for E3 excitation is observed in this work, but an upper limit is placed on the E3 matrix element to the lowest octupole band.

Multiple chiral bands in 137 Nd

Abstract: Two new bands have been identified in $$^{137}$$ Nd from a high-statistics JUROGAM II gamma-ray spectroscopy experiment. Constrained density functional theory and particle rotor model calculations are used to assign configurations and investigate the band properties, which are well described and understood. It is demonstrated that these two new bands can be interpreted as chiral partners of previously known three-quasiparticle positive- and negative-parity bands. The newly observed chiral doublet bands in $$^{137}$$ Nd represent an important support to the existence of multiple chiral bands in nuclei. The present results constitute the missing stone in the series of Nd nuclei showing multiple chiral bands, which becomes the most extended sequence of odd–even and even-even nuclei presenting multiple chiral bands in the Segre chart.

Novel Excitation Modes in Nuclei: Experimental and Theoretical Investigation on Multiple Chiral Doublets

Abstract: As a microscopic quantal many-body system, the structure of atomic nucleus is understood by measuring and interpreting its responses to all kinds of probes. The responses manifest in different kind...

Toward a nuclear mass table with the continuum and deformation effects: even-even nuclei in the nuclear chart

Abstract: The aim of this work is to develop the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) theory based on the point-coupling density functionals and extend it to provide a unified description for all even-even nuclei in the nuclear chart by overcoming all possible challenges. The nuclear superfluidity is considered via Bogoliubov transformation. Densities and potentials are expanded in terms of Legendre polynomials to include the axial deformation degrees of freedom. Sophisticated relativistic Hartree-Bogoliubov equations in coordinate space are solved in the DiracWoods-Saxon basis to consider the continuum effects. Numerical checks are performed from light nuclei to heavy nuclei. The techniques to construct the DRHBc mass table for even-even nuclei are explored. The DRHBc theory is extended to study heavier nuclei beyond magnesium isotopes. Taking Nd isotopes as examples, the experimental binding energies, two-neutron separation energies, quadrupole deformations, and charge radii are reproduced rather well. The deformation and continuum play essential roles in the description of nuclear masses and prediction of drip-line nuclei. By examining the single-particle levels in the canonical basis and their contributions to the total density, the thickness of the neutron skin, the particles number in continuum, and the Coulomb barrier, the exotic structures including the neutron skin and the proton radioactivity are predicted.

Effective field theory for triaxially deformed odd-mass nuclei

Abstract: The effective field theory for collective rotations of triaxially deformed nuclei is generalized to odd-mass nuclei by including the angular momentum of the valence nucleon as an additional degree of freedom. The Hamiltonian is constructed up to next-to-leading order within the effective field theory formalism. The applicability of this Hamiltonian is examined by describing the wobbling bands observed in the lutetium isotopes $^{161,163,165,167}$Lu. It is found that by taking into account the next-to-leading order corrections, quartic in the rotor angular momentum, the wobbling energies $E_{\textrm{wob}}$ and spin-rotational frequency relations $\omega(I)$ are better described than with the leading order Hamiltonian.

Triaxiality-related nuclear phenomena in the A ≈ 100 mass region

Abstract: Solid experimental evidence for triaxial nuclear shape is difficult to obtain and is quite rare. Such evidence can be provided by the phenomena of chiral rotation and wobbling motion, as these can occur only in triaxially deformed nuclei. Although nuclear chirality is well documented in different mass regions, experimental evidence for multiple chiral bands as well as for wobbling motion has been reported so far only in a few nuclei. Pd and Rh nuclei in the A ≈ 100 mass region have been recently studied, and transverse wobbling motion as well as multiple chiral band structures were identified for the first time in this region. These observations provide experimental evidence for the predicted triaxial shape in this mass region, and new data which enable a better understanding of the studied phenomena.

Multiple chiral bands in $^{137}$Nd

Abstract: Two new bands have been identified in $^{137}$Nd from a high-statistics JUROGAM II gamma-ray spectroscopy experiment Constrained density functional theory and particle rotor model calculations are used to assign configurations and investigate the band properties, which are well described and understood It is demonstrated that these two new bands can be interpreted as chiral partners of previously known three-quasiparticle positive- and negative-parity bands The newly observed chiral doublet bands in $^{137}$Nd represent an important support to the existence of multiple chiral bands in nuclei The present results constitute the missing stone in the series of Nd nuclei showing multiple chiral bands, which becomes the most extended sequence of nuclei presenting multiple chiral bands in the Segr\'e chart