Reflection Asymmetric Relativistic Mean Field Approach and Its Application to the Octupole Deformed Nucleus ^226Ra

A reflection asymmetric relativistic mean field （RAS-RMF） approach is developed by expanding the equations of motion for both the nucleons and the mesons on the eigenfunctions of the two-centre harmonic-oscillator potential. The efficiency and reliability of the RAS-RMF approach are demonstrated in its application to the well-known octupole deformed nucleus 226Ra and the available data, including the binding energy and the deformation parameters, are well reproduced.

超重核的壳结构

在相对论连续谱Hartree Bogoliubov(RCHB)理论框架下,在质子数Z=100—140和中子数N=Z+30—2Z+32等偶偶核中进行了超重球形双幻核的探索.采用的有效相互作用为NL1,NL3,NLSH,TM1,TW 99,DD ME1,PK1和PK1R.基于对双核子分离能(S2p和S2n)、双核子能隙(δ2p和δ2n)、壳修正能量(Epshell)、对能(Eppair和Enpair)和有效对能隙(Δp和Δn)等物理量和能shell和En级结构的分析,预言了可能的质子幻数和中子幻数,并观察到在超重核区壳的弱化现象.

Spurious Shell Closures in the Relativistic Mean Field Model

Following a previous systematic theoretical study of the ground-state properties of over 7000 nuclei from the proton drip line to the neutron drip line in the relativistic mean field model [Prog. Theor. Phys. 113 （2005） 785], which is in fair agreement with existing experimental data, we observe a few spurious shell closures, i.e. proton shell closures at Z = 58 and Z = 92. These spurious shell closures are found to persist in all the effective forces of the relativistic mean field model, e.g. TMA, NL3, PKDD and DD-ME2.

Tetraquark and Pentaquark Systems in Lattice QCD

We study multi-quark systems in lattice QCD. First, we revisit and summarize our accurate mass measurements of low-lying 5Q states with J = 1/2 and I = 0 in both positive- and negative-parity channels in anisotropic lattice QCD. The lowest positive-parity 5Q state is found to have a large mass of about 2.24 GeV after the chiral extrapolation. To single out the compact 5Q state from NK scattering states, we use the hybrid boundary condition (HBC), and find no evidence of the compact 5Q state below 1.75 GeV in the negative-parity channel. Second, we study the multi-quark potential in lattice QCD to clarify the inter-quark interaction in multi-quark systems. The 5Q potential V5Q for the QQ--QQ system is found to be well described by the “OGE Coulomb plus multi-Y Ansatz”: The sum of the one-gluon-exchange (OGE) Coulomb term and the multi-Y-type linear term based on the flux-tube picture. The 4Q potential V4Q for the QQ- system is also described by the OGE Coulomb plus multi-Y Ansatz, when QQ and are well separated. The 4Q system is described as a “two-meson” state with disconnected flux tubes, when the nearest quark and antiquark pair are spatially close. We observe a lattice-QCD evidence for the “flip-flop”, i.e., the fluxtube recombination between the connected 4Q state and the “two-meson” state. On the confinement mechanism, the lattice QCD results indicate the flux-tube-type linear confinement in multi-quark hadrons. Finally, we propose a proper quark-model Hamiltonian based on the lattice QCD results.

利用强子探针研究奇特原子核的点质子分布半径及强子探针效应

We report the charge-changing cross sections(σ_(cc))of 24 p-shell nuclides on both hydrogen and carbon at about 900A MeV,of which^(8,9)Li,^(10–12)Be,^(10,14,15)B,^(14,15,17–22)N and^(16)O on hydrogen and^(8,9)Li on carbon are for the first time.Benefiting from the data set,we found a new and robust relationship between the scaling factor of the Glauber model calculations and the separation energies of the nuclei of interest on both targets.This allows us to deduce proton radii(R_p)for the first time from the cross sections on hydrogen.Nearly identical R_p values are deduced from both target data for the neutron-rich carbon isotopes;however,the R_p from the hydrogen target is systematically smaller in the neutron-rich nitrogen isotopes.This calls for further experimental and theoretical investigations.

Coexistence of cluster and shell-model aspects in nuclear systems

We discuss cluster phenomena in light nuclei. As examples of typical cluster structures, we first review cluster structures of 12C, 16O, and 20Ne, and then introduce some topics of cluster phenomena in light neutron-rich nuclei such as Be and C isotopes. A particular attention is paid on coexistence of cluster and shell-model aspects.

Pion Effect of Nuclear Matter in a Chiral Sigma Model

We develop a new framework for the study of the nuclear matter based on the linear sigma model. We introduce a completely new viewpoint on the treatment of the nuclear matter with the inclusion of the pion. We extend the relativistic chiral mean field model by using the similar method in the tensor optimized shell model. We also regulate the pion-nucleon interaction by considering the form-factor and short range repulsion effects. We obtain the equation of state of nuclear matter and study the importance of the pion effect.

Dynamic nuclear self-polarization of Ⅲ–Ⅴsemiconductors

Ⅲ–Ⅴ semiconductors exhibit dynamic nuclear self-polarization(DYNASP) owing to the contact hyperfine interaction(HFI) between optically excited conduction electrons and lattice nuclei. In the self-polarization process at a low temperature, electron spin state and the nuclear polarization(magnetization) exchange a positive feedback, increasing energy splitting of the conduction electron states, thereby a large nuclear polarization. This phenomenon was theoretically predicted previously for conduction electrons excited linearly and elliptically polarized light. The polarization of the conduction electrons was represented by a parameter α in a formula for nuclear polarization(Eq.(9) in Ref. [1]); however, the effect of external magnetic fields on the nuclear polarization was not considered. Therefore, this study introduces this effect by further extending the previous studies. Herein, α′represents the combination of the effects of elliptically polarized electrons and an external magnetic field, which is used in the equations presented in previous studies. When α′ = 0, a large nuclear polarization is obtained below critical temperature Tc, but no polarization occurs above Tc. When α′ > 0, the nuclear polarization is enhanced above Tc. Below Tc, the nuclear polarization follows a hysteresis curve when α′ is partially manipulated by adjusting the degree of the polarization of the exciting laser.

Novel evidence for the σ-bond linear-chain molecular structure in ^(14)C

A multi-nucleon transfer and cluster decay experiment,^(7)Li(^(11)B,^(14)C^(*)→α+^(10)Be)α,is conducted at an incident beam energy of 55 MeV.This reaction channel has a significantly large 0-value,which favors populating the high lying resonant states in ^(14)C.The decay paths,from these resonances to various states of the final nucleus ^(10) Be,can be selected,owing to the experimentally achieved optimal resolution of the Q-value spectrum.A number of resonant states are reconstructed from the forward emitting 10Be+α fragments,and their major molecular structures can be detected according to the selective decay paths and relative decay widths.A state at 22.4(2)MeV validates the previously measured and theoretically predicted band head of the positive-parity σ-bond linear-chain mo-lecular band.Two additional resonances at 22.9(2)and 24.2(2)MeV are identified and consistent with the predicted 2^(+) and 4^(+) members of the same molecular band,thus providing novel evidences for the existence of the exotic clustering chain structure in neutron-rich carbon isotopes.A few high energy resonances,which also indicate the presence of the σ-bond molecular structure,are observed;however,further studies are still required to clarify their ascription in band systematics.

Development of Polarized HD Target for Future LEPS Experiments at SPring-8

We are carrying out hadron photoproduction experiments by using polarized photon beams at SPring-8 in Japan. In 2005,we started developing a polarized HD target for future experiments using both the polarized photon beams and the polarized target. The polarized HD target is an idealistic target for experiments observing reactions with small cross sections because the HD does not include heavy nuclei which produce many background events. The measurement of double polarization asymmetries is expected to give much important information to investigate the nucleon hidden structure,hadron photoproduction dynamics,and exotic hadron property. We report on the present status of the development of the polarized HD target at RCNP.

Light meson emissions of selected charmonium-like states within compact tetraquark configurations

We adopt the quark pair creation model to investigate the light meson emissions of several charmoniumlike states.The quark pair creation model is applied to four-body systems,and we calculate the pion/kaon emissions of X(4700),Z_(c)(4430),Y(4230),Y(4360),Y(4390),and Y(4660)within compact tetraquark configurations.We find that the pion/kaon decay widths of X(4700)and Z_(c)(4430)the resonances Y(4230),Y(4360),Y(4390),and Y(4660)cay behaviors will provide useful information for future experimental searches and theoretical interpretations.

Production of d_(NΩ)dibaryon in kaon induced reactions

In this paper,we propose to investigate the d_(NΩ)dibaryon production in the K-p-→d_(NΩ)≡0 process by utilizing a kaon beam with a typical momentum of approximately 10 GeV,which may be available at COMPASS,OKA@U-70,and SPS@CERN.The cross sections for K-p-→d_(NΩ)=O are estimated,and in particular,the magnitude of the cross sections is evaluated to be several hundred nanobarns at Pk=20 GeV.Considering that the d_(NΩ)dibaryon dominantly decays into≡Λand≡∑,we also estimate the cross sections for K-p→≡0Λ≡0 and K~p→≡-∑+≡0,where the d_(NΩ)dibaryon can be observed in the invariant mass distributions of≡0Λand≡-∑+,respectively.

Nonlocalized clustering and evolution of cluster structure in nuclei

We explain various facets of the THSR(Tohsaki-Horiuchi Schuck-Ropke)wave function.We first discuss the THSR,wave function as a wave function of cluster-gas state,since the THSR,wave function was originally introduced to elucidate the 3a-condensate-like character of the Hoyle state(O2^+ state)of 12C.We briefly review the cluster-model studies of the Hoyle state in 1970’s in order to explain how there emerged the idea to assign the a condensate character to the Hoyle state.We then explain that the THSR wave function can describe very well also non-gaslike ordinary cluster states with spatial localization of clusters.This fact means that the dynamical motion of clusters is of nonlocalized nature just as in gas-like states of clusters and the localization of clusters is due to the inter-cluster Pauli principle which is against the close approach of two clusters.The nonlocalized cluster dynamics is formulated by the container model of cluster dynamics.The container model describes gas-like state and non-gaslike states as the solutions of the Hill Wheeler equation with respect to the size parameter of THSR wave function which is just the size parameter of the container.When we notice that fact that the THSR wave function with the smallest value of size parameter is equivalent to the shell-model wave function,we see that the container model describes the evolution of cluster structure from the ground state with shell-model structure up to the gas-like cluster state via ordinary non-gaslike cluster states.For the description of various cluster structure,more generation of THSR wave function have been introduced and we review some typical examples with their actual applications.

Finite particle number description of neutron matter using the unitary correlation operator and high-momentum pair methods

Using bare Argonne V4'(AV4'),V6'(AV6'),and V8'(AV8')nucleon–nucleon(NN)interactions,the nuclear equations of state(EOSs)for neutron matter are calculated with the unitary correlation operator and high-momentum pair methods.Neutron matter is described using a finite particle number approach with magic number N=66 under a periodic boundary condition.The central short-range correlation originating from the short-range repulsion in the NN interaction is treated by the unitary correlation operator method(UCOM),and the tensor correlation and spin-orbit effects are described by the two-particle two-hole(2p2h)excitations of nucleon pairs,where the two nucleons with a large relative momentum are regarded as a high-momentum(HM)pair.With increasing 2p2h configurations,the total energy per particle of the neutron matter is well-converged under this UCOM+HM framework.Comparing the results calculated with AV4',AV6',and AV8'NN interactions,we demonstrate the effects of the short-range correlation,tensor correlation,and spin-orbit coupling on the density dependence of the total energy per particle of neutron matter.Moreover,the contribution of each Hamiltonian component to the total energy per particle is discussed.The EOSs of neutron matter calculated within the present UCOM+HM framework agree with the calculations of six microscopic many-body theories,especially the auxiliary field-diffusion Monte Carlo calculations.

Level Crossing of N*(1535)-hole and η Modes and Partial Restoration of Chiral Symmetry in η-mesic Nuclei

We investigate the properties of the η-nucleus interaction by postulating the N*(1535) dominance for ηN system. Since the mass gap of N* and N is very close to the η meson mass,there is the possibility of the level crossing between the N*-h and η modes in finite density. We postulate the N*(1535) resonance for the ηN system and consider quite distinct N* properties in finite density which are predicted by two independent chiral models. We find that we can obtain clearer information on the in-medium N* properties and also on the η-nucleus interaction through the formation of the η-mesic nuclei by (π,N) reactions under the appropriate experimental conditions,which can be performed at existing and/or forthcoming facilities like J-PARC.

Origin of Dynamically Generated Baryon Rsonances

We study the origin of baryon resonances which are dynamically generated in the chiral unitary approach. We propose a natural renormalization scheme for the dynamical generation of resonances using the low energy chiral interaction and a general feature of the scattering theory. A deviation of a phenomenological scattering amplitude from the natural one is interpreted by an effective pole term interaction of genuine nature which can not be described by the meson-baryon dynamics,reminiscent of the CDD pole. Applying the present method to physical meson-baryon scatterings,we find that the Λ(1405) resonance is dominated by a meson-baryon component forming a KN-πΣ molecular-like structure,while the N(1535) resonance requires some pole contribution.

Anomalous Contributions in Kaon-photoproductions

We study kaon photoproduction from the nucleon. Using the photon beam asymmetry,we discuss the couplings of the K and K* mesons with baryons. In previous studies of photoproductions,the K* coupling strength has been treated as parameters to reproduce experimental data. Here instead we propose to use the coupling strength which is derived from a microscopic description. By including a higher order loop contribution induced by the QCD anomaly,we demonstrate that the experimental data can be explained well. The use of a microscopic description enables us a better understanding of the reaction dynamics which provides further basis of hadron dynamics.

One-pion-exchange potential with contact terms from lattice QCD simulations

Pion-mass-dependent nucleon-nucleon(NN)potentials are obtained in terms of the one-pion exchange and contact terms from the latest lattice QCD simulations of the two-nucleon system.They assume the forms of the leading order(LO)NN potential from the chiral effective field theory and thus are referred to as the LO chiral potential in this study.We extract the coefficients of contact terms and cut-off momenta in these potentials,for the first time,by fitting the phase shifts of 1S0 and 3S1 channels obtained from the HALQCD collaboration with various pion masses from 468.6 to 1170.9 MeV.The low-energy constants in the 1S0 and 3S1 channels become weaker and approach each other for larger pion masses.These LO chiral potentials are applied to symmetric nuclear and pure neutron matter within the Brueckner-Hartree-Fock method.Presently,however,we do not yet have the information of the P-wave NN interaction to be provided by the lattice QCD simulations for a complete description of nuclear matter.Our results enhance understanding of the development of nuclear structure and nuclear matter by controlling the contribution of the pionic effect and elucidate the role of chiral symmetry of the strong interaction in complex systems.