Browsing by Author "Meng, Jie"
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- ItemChiral geometry and rotational structure for ¹³⁰Cs in the projected shell model(Elsevier, 2018) Chen, F. Q.; Meng, Jie; Zhang, S. Q.The projected shell model with configuration mixing for nuclear chirality is developed and applied to the observed rotational bands in the chiral nucleus 130Cs. For the chiral bands, the energy spectra and electromagnetic transition probabilities are well reproduced. The chiral geometry illustrated in the Kplotand the azimuthalplotis confirmed to be robust against the configuration mixing. The other rotational bands are also described in the same framework.
- ItemConsistency between SU(3) and SU(2) covariant baryon chiral perturbation theory for the nucleon mass(Elsevier, 2017) Ren, Xiu-Lei; Alvarez-Ruso, L.; Geng, Li-Sheng; Ledwig, Tim; Meng, Jie; Vacas, M. J. VicenteTreating the strange quark mass as a heavy scale compared to the light quark mass, we perform a matching of the nucleon mass in the SU(3) sector to the two-flavor case in covariant baryon chiral perturbation theory. The validity of the 19 low-energy constants appearing in the octet baryon masses up to next-to-next-to-next-to-leading order  is supported by comparing the effective parameters (the combinations of the 19 couplings) with the corresponding low-energy constants in the SU(2) sector . In addition, it is shown that the dependence of the effective parameters and the pion-nucleon sigma term on the strange quark mass is relatively weak around its physical value, thus providing support to the assumption made in Ref.  that the SU(2) baryon chiral perturbation theory can be applied to study nf = 2+1 lattice QCD simulations as long as the strange quark mass is close to its physical value.
- ItemEffective field theory for collective rotations and vibrations of triaxially deformed nuclei(American Physical Society, 2018) Chen, Q. B.; Kaiser, N.; Meibner, Ulf G.; Meng, JieThe effective field theory (EFT) for triaxially deformed even-even nuclei is generalized to include the vibrational degrees of freedom. The pertinent Hamiltonian is constructed up to next-to-leading order (NLO). The leading-order part describes the vibrational motion, and the NLO part couples rotations to vibrations. The applicability of the EFT Hamiltonian is examined through the description of the energy spectra of the ground state bands, γ bands, and K=4 bands in the 108,110,112Ru isotopes. It is found that, by taking into account the vibrational degrees of freedom, the deviations for high-spin states in the γ band observed in the EFT with only rotational degrees of freedom disappear. This supports the importance of including vibrational degrees of freedom in the EFT formulation for the collective motion of triaxially deformed nuclei.
- ItemEffects of tensor forces in nuclear spin–orbit splittings from ab initio calculations(Elsevier, 2018) Shen, Shihang; Liang, Haozhao; Meng, Jie; Ring, Peter; Zhang, ShuangquanA systematic and specific pattern due to the effects of the tensor forces is found in the evolution of spin–orbit splittings in neutron drops. This result is obtained from relativistic Brueckner–Hartree–Fock theory using the bare nucleon–nucleon interaction. It forms an important guide for future microscopic derivations of relativistic and nonrelativistic nuclear energy density functionals.
- ItemEvolution from quasivibrational to quasirotational structure in 155Tm and yrast 27/2− to 25/2− energy anomaly in the A ≈ 150 mass region(American Physical Society, 2019) Liu, L.; Wang, S. Y.; Wang, S.; Hua, H.; Zhang, S. Q.; Meng, Jie; Bark, R. A.; Wyngaardt, S. M.; Qi, B.; Sun, D. P.; Liu, C.; Li, Z. Q.; Jia, H.; Li, X. Q.; Xu, C.; Li, Z. H.; Sun, J. J.; Zhu, L. H.; Jones, P.; Lawrie, E. A.; Lawrie, J. J.; Wiedeking, M.; Bucher, T. D.; Dinoko, T.; Makhathini, L.; Majola, S. N. T.; Noncolela, S. P.; Shirinda, O.; Gal, J.; Kalinka, G.; Molnar, J.; Nyako, B. M.; Timar, J.; Juhasz, K.; Arogunjo, M.Excited states in 155Tm have been populated via the reaction 144Sm(16O, p4n)155Tm at a beam energy of 118 MeV. The ground-state band has been extended and a new side band of the ground-state band is identified. E-GOS curves and potential energy surface calculations are employed to discuss the structure evolution of the ground-state band. The newly observed side band in 155Tm is discussed based on the spin/energy systematics. In particular, the phenomenon of seniority inversion is proposed in 155Tm, and a systematic study of this phenomenon in the A ≈ 150 mass region is performed.
- ItemFully self-consistent relativistic Brueckner-Hartree-Fock theory for finite nuclei(American Physical Society, 2017) Shen, Shihang; Liang, Haozhao; Meng, Jie; Ring, Peter; Zhang, ShuangquanStarting from the relativistic form of the Bonn potential as a bare nucleon-nucleon interaction, the full relativistic Brueckner-Hartree-Fock (RBHF) equations are solved for finite nuclei in a fully self-consistent basis. This provides a relativistic ab initio calculation of the ground state properties of finite nuclei without any free parameters and without three-body forces. The convergence properties for the solutions of these coupled equations are discussed in detail for the example of the nucleus ¹⁶O. The binding energies, radii, and spin-orbit splittings of the doubly magic nuclei ⁴He, ¹⁶O, and ⁴⁰Ca are calculated and compared with the earlier RBHF calculated results in a fixed Dirac Woods-Saxon basis and other nonrelativistic ab initio calculated results based on pure two-body forces.
- ItemInfluence of pairing correlations on the radius of neutron-rich nuclei(American Physical Society, 2017) Zhang, Ying; Chen, Ying; Meng, Jie; Ring, PeterThe influence of pairing correlations on the neutron root mean square (rms) radius of nuclei is investigated in the framework of self-consistent Skyrme Hartree-Fock-Bogoliubov calculations. The continuum is treated appropriately by the Green's function techniques. As an example the nucleus ¹²⁴Zr is treated for a varying strength of pairing correlations. We find that, as the pairing strength increases, the neutron rms radius first shrinks, reaches a minimum, and beyond this point it expands again. The shrinkage is due to the the so-called pairing antihalo effect, i.e., due to the decrease of the asymptotic density distribution with increasing pairing. However, in some cases, increasing pairing correlations can also lead to an expansion of the nucleus due to a growing occupation of so-called halo orbits, i.e., weakly bound states and resonances in the continuum with low-ℓ values. In this case, the neutron radii are extended just by the influence of pairing correlations, since these halo orbits cannot be occupied without pairing. The term “antihalo effect” is not justified in such cases. For a full understanding of this complicated interplay, self-consistent calculations are necessary.
- ItemMultiple chiral doublets in four-j shells particle rotor model : five possible chiral doublets in ¹³⁶₆₀Nd₇₆(Elsevier, 2018) Chen, Q. B.; Lv, B. F.; Petrache, C. M.; Meng, JieA particle rotor model, which couples nucleons in four single-jshells to a triaxial rotor core, is developed to investigate the five pairs of nearly degenerate doublet bands recently reported in the even-even nucleus 136Nd. The experimental energy spectra and available B(M1)/B(E2)values are successfully reproduced. The angular momentum geometries of the valence nucleons and the core support the chiral rotation interpretations not only for the previously reported chiral doublet, but also for the other four candidates. Hence, 136Nd is the first even-even candidate nucleus in which the multiple chiral doublets exist. Five pairs of chiral doublet bands in a single nucleus is also a new record in the study of nuclear chirality.
- ItemNuclear matrix element of neutrinoless double-β decay : relativity and short-range correlations(American Physical Society, 2017) Song, L. S.; Yao, J. M.; Ring, P.; Meng, JieBackground:The discovery of neutrinoless double-β (0νββ) decay would demonstrate the nature of neutrinos, have profound implications for our understanding of matter-antimatter mystery, and solve the mass hierarchy problem of neutrinos. The calculations for the nuclear matrix elements M0ν of 0νββ decay are crucial for the interpretation of this process. Purpose: We study the effects of relativity and nucleon-nucleon short-range correlations on the nuclear matrix elements M0ν by assuming the mechanism of exchanging light or heavy neutrinos for the 0νββ decay. Methods:The nuclear matrix elements M0ν are calculated within the framework of covariant density functional theory, where the beyond-mean-field correlations are included in the nuclear wave functions by configuration mixing of both angular-momentum and particle-number projected quadrupole deformed mean-field states. Results: The nuclear matrix elements M0ν are obtained for ten 0νββ-decay candidate nuclei. The impact of relativity is illustrated by adopting relativistic or nonrelativistic decay operators. The effects of short-range correlations are evaluated. Conclusions: The effects of relativity and short-range correlations play an important role in the mechanism of exchanging heavy neutrinos though the influences are marginal for light neutrinos. Combining the nuclear matrix elements M0ν with the observed lower limits on the 0νββ-decay half-lives, the predicted strongest limits on the effective masses are |⟨mν⟩|<0.06 eV for light neutrinos and ∣⟨mֿ¹νh⟩∣ֿ¹>3.065×10⁸ GeV for heavy neutrinos.
- ItemNuclear quantum shape-phase transitions in odd-mass systems(American Physical Society, 2018) Quan, S.; Li, Z. P.; Vretenar, D.; Meng, JieMicroscopic signatures of nuclear ground-state shape-phase transitions in odd-mass Eu isotopes are explored starting from excitation spectra and collective wave functions obtained by diagonalization of a core-quasiparticle coupling Hamiltonian based on energy density functionals. As functions of the physical control parameter—the number of nucleons—theoretical low-energy spectra, two-neutron separation energies, charge isotope shifts, spectroscopic quadrupole moments, and E2 reduced transition matrix elements accurately reproduce available data and exhibit more-pronounced discontinuities at neutron number N=90 compared with the adjacent even-even Sm and Gd isotopes. The enhancement of the first-order quantum phase transition in odd-mass systems can be attributed to a shape polarization effect of the unpaired proton which, at the critical neutron number, starts predominantly coupling to Gd core nuclei that are characterized by larger quadrupole deformation and weaker proton pairing correlations compared with the corresponding Sm isotopes.
- ItemReexamining nuclear chiral geometry from the orientation of the angular momentum(American Physical Society, 2018) Chen, Q. B.; Meng, JieThe paradox on the previous interpretation for the nuclear chiral geometry based on the effective angle has been clarified by reexamining the system with the particle-hole configuration π(1h11/2)1⊗ν(1h11/2)−1 and a rotor with the deformation parameter γ=30∘. It is found that the paradox is caused by the fact that the angular momentum of the rotor is much smaller than those of the proton and the neutron near the bandhead. Hence, it does not support a chiral rotation interpretation near the bandhead. The nuclear chiral geometry based on the effective angle makes sense only when the angular momentum of the rotor becomes comparable with those of the proton and neutron for a particular range of spin values.
- ItemRelativistic Brueckner-Hartree-Fock theory for neutron drops(American Physical Society, 2018) Shen, Shihang; Liang, Haozhao; Meng, Jie; Ring, Peter; Zhang, ShuangquanNeutron drops confined in an external field are studied in the framework of relativistic Brueckner-Hartree-Fock theory using the bare nucleon-nucleon interaction. The ground-state energies and radii of neutron drops with even numbers from N=4 to N=50 are calculated and compared with results obtained from other nonrelativistic ab initio calculations and from relativistic density functional theory. Special attention has been paid to the magic numbers and to the subshell closures. The single-particle energies are investigated and the monopole effect of the tensor force on the evolutions of the spin-orbit and the pseudospin-orbit splittings is discussed. The results provide interesting insights into neutron-rich systems and can form an important guide for future density functionals.
- ItemRelativistic Brueckner-Hartree-Fock theory in nuclear matter without the average momentum approximation(American Physical Society, 2018) Tong, Hui; Ren, Xiu-Lei; Ring, Peter; Shen, Shi-Hang; Wang, Si-Bo; Meng, JieBrueckner-Hartree-Fock theory allows one to derive the G matrix as an effective interaction between nucleons in the nuclear medium. It depends on the center-of-mass momentum P of the two particles and on the two relative momenta q and q′ before and after the scattering process. In the evaluation of the total energy per particle in nuclear matter, usually the angle-averaged center-of-mass momentum approximation has been used. We derive in detail the exact expressions of the angular integrations of the momentum P within relativistic Brueckner-Hartree-Fock (RBHF) theory, especially for the case of asymmetric nuclear matter. In order to assess the reliability of the conventional average momentum approximation for the binding energy, the saturation properties of symmetric and asymmetric nuclear matter are systematically investigated based on the realistic Bonn nucleon-nucleon potential. It is found that the exact treatment of the center-of-mass momentum leads to non-negligible contributions to the higher order physical quantities. The correlations between the symmetry energy Esym, the slope parameter L, and the curvature Ksym of the symmetry energy are investigated. The results of our RBHF calculations for the bulk parameters characterizing the equation of state are compared with recent constraints extracted from giant monopole resonance and isospin diffusion experiments.
- ItemSelf-consistent relativistic quasiparticle random-phase approximation and its applications to charge-exchange excitations(American Physical Society, 2017) Niu, Z. M.; Niu, Y. F.; Liang, H. Z.; Long, W. H.; Meng, JieThe self-consistent quasiparticle random-phase approximation (QRPA) approach is formulated in the canonical single-nucleon basis of the relativistic Hatree–Fock–Bogoliubov (RHFB) theory. This approach is applied to study the isobaric analog states (IASs) and Gamow–Teller resonances (GTRs) by taking Sn isotopes as examples. It is found that self-consistent treatment of the particle-particle residual interaction is essential to concentrate the IAS in a single peak for open-shell nuclei and the Coulomb exchange term is very important to predict the IAS energies. For the GTR, the isovector pairing can increase the calculated GTR energy, while the isoscalar pairing has an important influence on the low-lying tail of the Gamow–Teller transition.
- ItemSolving Dirac equations on a 3D lattice with inverse Hamiltonian and spectral methods(American Physical Society, 2017) Ren, Z. X.; Zhang, S. Q.; Meng, JieA new method to solve the Dirac equation on a 3D lattice is proposed, in which the variational collapse problem is avoided by the inverse Hamiltonian method and the fermion doubling problem is avoided by performing spatial derivatives in momentum space with the help of the discrete Fourier transform, i.e., the spectral method. This method is demonstrated in solving the Dirac equation for a given spherical potential in a 3D lattice space. In comparison with the results obtained by the shooting method, the differences in single-particle energy are smaller than 10ֿ⁻⁴ MeV, and the densities are almost identical, which demonstrates the high accuracy of the present method. The results obtained by applying this method without any modification to solve the Dirac equations for an axial-deformed, nonaxial-deformed, and octupole-deformed potential are provided and discussed
- ItemSpectroscopic study of the possibly triaxial transitional nucleus 75Ge(American Physical Society, 2018) Niu, C. Y.; Dai, A. C.; Xu, C.; Hua, H.; Zhang, S. Q.; Wang, S. Y.; Bark, R. A.; Meng, Jie; Wang, C. G.; Wu, X. G.; Li, X. Q.; Li, Z. H.; Wyngaardt, S. M.; Zang, H. L.; Chen, Z. Q.; Wu, H. Y.; Xu, F. R.; Ye, Y. L.; Jiang, D. X.; Han, R.; Li, C. G.; Chen, X. C.; Liu, Q.; Feng, J.; Yang, B.; Li, Z. H.; Wang, S.; Sun, D. P.; Liu, C.; Li, Z. Q.; Zhang, N. B.; Guo, R. J.; Li, G. S.; He, C. Y.; Zheng, Y.; Li, C. B.; Chen, Q. M.; Zhong, J.; Zhou, W. K.; Zhu, B. J.; Deng, L. T.; Liu, M. L.; Wang, J. G.; Jones, P.; Lawrie, E. A.; Lawrie, J. J.; Sharpey-Schafer, J. F.; Wiedeking, M.; Majola, S. N. T.; Bucher, T. D.; Dinoko, T.; Magabuka, B.; Makhathini, L.; Mdletshe, L.; Khumalo, N. A.; Shirinda, O.; Sowazi, K.The collective structures of 75Ge have been studied for the first time via the 74Ge(α,2p1n) 75Ge fusionevaporation reaction. Two negative-parity bands and one tentative positive-parity band built on the νp1/2, νf5/2, and νg9/2 states, respectively, are established and comparedwith the structures in the neighboringN = 43 isotones. According to the configuration-constrained potential-energy surface calculations, a shape transition from oblate to prolate along the isotopic chain in odd-A Ge isotopes is suggested to occur at 75Ge. The properties of the bands in 75Ge are analyzed in comparison with the triaxial particle rotor model calculations.
- ItemSpin symmetry in the Dirac sea derived from the bare nucleon–nucleon interaction(Elsevier, 2018) Shen, Shihang; Liang, Haozhao; Meng, Jie; Ring, Peter; Zhang, ShuangquanThe spin symmetry in the Dirac sea has been investigated with relativistic Brueckner–Hartree–Fock theory using the bare nucleon–nucleon interaction. Taking the nucleus 16O as an example and comparing the theoretical results with the data, the definition of the single-particle potential in the Dirac sea is studied in detail. It is found that if the single-particle states in the Dirac sea are treated as occupied states, the ground state properties are in better agreement with experimental data. Moreover, in this case, the spin symmetry in the Dirac sea is better conserved and it is more consistent with the findings using phenomenological relativistic density functionals.
- ItemStrength of tensor forces from neutron drops in ab initio relativistic Brueckner-Hartree-Fock theory(American Physical Society, 2019) Wang, Sibo; Tong, Hui; Zhao, Pengwei; Meng, JieThe evolution of spin-orbit splittings of neutron drops along with the neutron number and its connection with the tensor-force strength have been investigated systematically for different external fields in the relativistic Brueckner-Hartree-Fock (RBHF) and relativistic Hartree-Fock (RHF) theories. Based on the RHF functional PKO1, it is found that a good consistency between the RBHF and RHF results for the total energies can be obtained only for those neutron drops whose central densities are close to the saturation density of nuclear matter. Nevertheless, by rescaling the density dependence of the RHF functional, the RBHF total energies of neutron drops in different external fields can be well reproduced. The optimized tensor-force strength λ in the RHF theory, which reproduces the microscopic RBHF spin-orbit splittings, is running with the strength of the external fields of neutron drops. This provides an important guide for future determination of tensor forces in nuclear energy density functionals based on microscopic ab initio calculations.
- ItemTowards the improvement of spin-isospin properties in nuclear energy density functionals(IOP Publishing, 2016) Roca-Maza, X.; Colo, G.; Liang, H. Z.; Meng, Jie; Ring, P.; Sagawa, H.; Zhao, P. W.We address the problem of improving existing nuclear Energy Density Functionals (EDFs) in the spin-isospin channel. For that, we propose two different ways. The first one is to carefully take into account in the fitting protocol some of the key ground state properties for an accurate description of the most studied spin-isospin resonances: the Gamow-Teller Resonance (GTR) . The second consists in providing a strategy to build local covariant EDF keeping the main features from their non-local counterparts . The RHF model based on a Lagrangian where heavy mesons carry the nuclear effective interaction have been shown to be successful in the description of spin-isospin resonances .
- ItemUnderstanding the chiral geometry with K-Plot and Azimuthal-Plot(Jagellonian University, 2018) Chen, F. Q.; Meng, JieThe chiral geometry of the angular momentum in the intrinsic frame is extracted from angular momentum projected wave functions in the laboratory frame by the K-Plot and Azimuthal-Plot. The method is demonstrated by an application to the chiral doublet bands in 128Cs, based on the standard pairing-plus-quadrupole Hamiltonian. The observed energy spectra and the electromagnetic transitions are well-reproduced, and the K-Plot and Azimuthal-Plot obtained give evolution of angular momentum geometry with spin, by which the chirality is demonstrated.