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Y. Suzuki

Publications and source records attributed to Y. Suzuki.

251 records · Page 14Linked to original sources
arXiv1999

Single-Particle Spin-Orbit Strengths of the Nucleon and Hyperons by SU6 Quark-Model

The quark-model hyperon-nucleon interaction suggests an important antisymmetric spin-orbit component. It is generated from a color analogue of the Fermi-Breit interaction dominating in the one-gluon exchange process between quarks. We discuss the strength S_B of the single-particle spin-orbit potential, following the Scheerbaum's prescription. Using the SU6 quark-model baryon-baryon interaction which was recently developed by the Kyoto-Niigata group, we calculate NN, Lambda N and Sigma N G-matrices in symmetric nuclear matter and apply them to estimate the strength S_B. The ratio of S_B to the nucleon strength S_N =~ -40 MeV*fm^5 is (S_Lambda)/(S_N) =~ 1/5 and (S_Sigma)/(S_N) =~ 1/2 in the Born approximation. The G-matrix calculation of the model FSS modifies S_Lambda to (S_Lambda)/(S_N) =~ 1/12. For S_N and S_Sigma, the effect of the short-range correlation is comparatively weak against meson-exchange potentials with a short-range repulsive core. The significant reduction of the Lambda single-particle potential arises from the combined effect of the antisymmetric LS force, the flavor-symmetry breaking originating from the strange to up-down quark-mass difference, as well as the effect of the short-range correlation. The density dependence of S_B is also examined.

nucl-th↗
arXiv1998

Signature of the existence of the positronium molecule

The positronium molecule (Ps$_2$) has not been experimentally observed yet because its tiny (4.5 eV) binding energy cannot be detected when the molecule annihilates by emitting two photons with energy of 0.51 MeV each. It is shown in this paper that the electric dipole transition between the recently found L=1 excited-state and the L=0 ground-state with its characteristic photon energy of 4.94 eV is a clear signature of the existence of the positronium molecule and the possibility of its experimental observation is realistic. The probability of this transition is about 17 % of the total decay rate. An other Coulomb four-body system containing positron, HPs (the positronium hydride or hydrogen positride), is also included for comparison.

physics.atom-ph↗
arXiv1998

Second bound state of the positronium molecule and biexcitons

A new, hitherto unknown bound state of the positronium molecule, with orbital angular momentum L=1 and negative parity is reported. This state is stable against autodissociation even if the masses of the positive and negative charges are not equal. The existence of a similar state in two-dimension has also been investigated. The fact that the biexcitons have a second bound state may help the better understanding of their binding mechanism.

cond-mat.mes-hall↗
arXiv1997

Exploration of resonances by analytic continuation in the coupling constant

The energy and the width of resonance states are determined by analytic continuation of bound-state energies as a function of the coupling constant (potential strength). The advantage of the method is that the existing techniques for calculation of bound states can be applied, without any modifications, to determine the position of resonances. Various numerical examples show the applicability of the method for three-body systems, including the excited states of the $^6$He and $^6$Li.

nucl-th↗
arXiv1997

Solution of few-body problems with the stochastic variational method: I. Central forces

This paper presents a fortran program to solve diverse few-body problems with the stochastic variational method. Depending on the available computational resources the program is applicable for $N=2-3-4-5-6-...$-body systems with $L=0$ total orbital momentum. The solution with the stochastic variational method is ``automatic'' and universal. One defines the system (number of particles, masses, symmetry, interaction, etc. ) and the program finds the ground state energy and wave function. The examples include nuclear (alpha particle: four-body, $^6$He: six-body), atomic (td$μ^-$ and $e^+e^-e^+e^-$) and subnuclear (the nucleon and the delta in a nonrelativistic quark model) systems. The solutions are accurate for excited states as well, and even the Efimov-states can be studied. The program is available from the author (e-mail:varga@rikaxp.riken.go.jp).

nucl-th↗
arXiv1997

New representation of orbital motion with arbitrary angular momenta

A new formulation is presented for a variational calculation of $N$-body systems on a correlated Gaussian basis with arbitrary angular momenta. The rotational motion of the system is described with a single spherical harmonic of the total angular momentum $L$, and thereby needs no explicit coupling of partial waves between particles. A simple generating function for the correlated Gaussian is exploited to derive the matrix elements. The formulation is applied to various Coulomb three-body systems such as $e^-e^-e^+, ttμ, tdμ$, and $αe^-e^-$ up to $L=4$ in order to show its usefulness and versatility. A stochastic selection of the basis functions gives good results for various angular momentum states.

nucl-th↗
arXiv1996

Stochastic variational method with noncentral forces

This paper extends the application of the stochastic variational method to noncentral interactions. Several examples are presented for three- and four-nucleon systems with realistic nuclear forces. The correlated Gaussians easily cope with the strong short range repulsion of the potential and the stochastic variational method efficiently selects the most important spin, isospin and orbital angular momentum components of the wave function. The examples confirm the usefulness and accuracy of the method.

nucl-th↗
arXiv1996

Microscopic description of light unstable nuclei with the stochastic variational method

The structure of the light proton and neutron rich nuclei is studied in a microscopic multicluster model using the stochastic variational method. This approach enables us to describe the weakly bound nature of these nuclei in a consistent way. Applications for various nuclei $^{6-9}$Li, $^7$Be, $^8$B, $^9$C, $^{9-10}$Be, $^{9-10}$B presented. The paper discusses the relation of this model to other models as well as the possible extension for p and sd shell nuclei.

nucl-th↗
arXiv1996

Occupation probability of harmonic-oscillator quanta for microscopic cluster-model wave functions

We present a new and simple method of calculating the occupation probability of the number of total harmonic-oscillator quanta for a microscopic cluster-model wave function. Examples of applications are given to the recent calculations including $α+n+n$-model for $^6$He, $α+t+n+n$-model for $^9$Li, and $α+α+n$-model for $^9$Be as well as the classical calculations of $α+p+n$-model for $^6$Li and $α+α+α$-model for $^{12}$C. The analysis is found to be useful for quantifying the amount of excitations across the major shell as well as the degree of clustering. The origin of the antistretching effect is discussed.

nucl-th↗
arXiv1996

Structure of the mirror nuclei $^9$Be and $^9$B in a microscopic cluster model

The structure of the mirror nuclei $^9$Be and $^9$B is studied in a microscopic $α+ α+ n$ and $α+ α+ p$ three-cluster model using a fully antisymmetrized 9-nucleon wave function. The two-nucleon interaction includes central and spin-orbit components and the Coulomb potential. The ground state of $^9$Be is obtained accurately with the stochastic variational method, while several particle-unbound states of both $^9$Be and $^9$B are investigated with the complex scaling method.The calculation for $^9$Be supports the recent identification for the existence of two broad states around 6.5 MeV, and predicts the $\frac{3}{2}^{-}_2$ and $\frac{5}{2}^{-}_2$ states at about 4.5 MeV and 8 MeV, respectively. The similarity of the calculated spectra of $^9$Be and $^9$B enables one to identify unknown spins and parities of the $^9$B states. Available data on electromagnetic moments and elastic electron scatterings are reproduced very well. The enhancement of the $E$1 transition of the first excited state in $^9$Be is well accounted for. The calculated density of $^9$Be is found to reproduce the reaction cross section on a Carbon target. The analysis of the beta decay of $^9$Li to $^9$Be clearly shows that the wave function of $^9$Be must contain a small component that cannot be described by the simple $α+ α+ n$ model. This small component can be well accounted for by extending a configuration space to include the distortion of the $α$-particle to $t+p$ and $h+n$ partitions.

nucl-th↗
arXiv1996

Local structure study about Co in YBa$_2$(Cu$_{1-x}$Co$_x$)$_3$O$_{7-δ}$ thin films using polarized XAFS

We have studied the local structure around Co in YBa$_2$(Cu$_{1-x}$Co$_x$)$_3$O$_{7-δ}$ thin films with three different concentrations: x=0.07, 0.10, 0.17, and in a PrBa$_2$(Cu$_{1-x}$Co$_x$)$_3$O$_{7-δ}$ thin film of concentration x=0.05 using the X-ray Absorption Fine Structure (XAFS) technique. Data were collected at the Co $K$-edge with polarizations both parallel and perpendicular to the film surface. We find that the oxygen neighbors are well ordered and shortened in comparison with YBCO Cu-O values to 1.80 Å and 1.87 Å in the $c$-axis and $ab$-plane, respectively. A comparison of further neighbors in the thin film and powder data show that these peaks in the film are suppressed in amplitude relative to the powder samples, which suggests there is more disorder and/or distortions of the Co environment present in the thin films.

cond-mat↗
arXiv1996

Coulomb Breakup Mechanism of Neutron-Halo Nuclei in a Time-Dependent Method

The mechanism of the Coulomb breakup reactions of the nuclei with neutron-halo structure is investigated in detail. A time-dependent Schrödinger equation for the halo neutron is numerically solved by treating the Coulomb field of a target as an external field. The momentum distribution and the post-acceleration effect of the final fragments are discussed in a fully quantum mechanical way to clarify the limitation of the intuitive picture based on the classical mechanics. The theory is applied to the Coulomb breakup reaction of $^{11}$Be + $^{208}$Pb. The breakup mechanism is found to be different between the channels of $j^π=\frac{1}{2}^{-}$ and $\frac{3}{2}^{-}$, reflecting the underlying structure of $^{11}$Be. The calculated result reproduces the energy spectrum of the breakup fragments reasonably well, but explains only about a half of the observed longitudinal momentum difference.

nucl-th↗
arXiv1995

Precise solution of few-body problems with stochastic variational method on correlated Gaussian basis

Precise variational solutions are given for problems involving diverse fermionic and bosonic $N=2-7$-body systems. The trial wave functions are chosen to be combinations of correlated Gaussians, which are constructed from products of the single-particle Gaussian wave packets through an integral transformation, thereby facilitating fully analytical calculations of the matrix elements. The nonlinear parameters of the trial function are chosen by a stochastic technique. The method has proved very efficient, virtually exact, and it seems feasible for any few-body bound-state problems emerging in nuclear or atomic physics.

nucl-th↗
arXiv1995

Precise solution of few-body problems with the stochastic variational method

A precise variational solution to $N$=2--6-body problems is reported. The trial wave functions are chosen to be combinations of correlated Gaussians, which facilitate a fully analytical calculation of the matrix elements. The nonlinear parameters of the trial function are selected by a stochastic method. Fermionic and bosonic few-body systems are investigated for interactions of different type. A comparison of the results with those available in the literature shows that the method is both accurate and efficient.

nucl-th↗
arXiv1994

Microscopic multicluster description of the neutron-rich helium isotopes

The neutron halo structure of $^{6}$He and of $^{8}$He is studied in a microscopic three-body and five-body model, respectively. Various cluster arrangements are included to embody a variety of correlations between the clusters. The intercluster wave function is determined with the stochastic variational method. The $^{6}$He and $^{8}$He energies are reproduced with the same effective force very well. The radii and densities are compared with the results of empirical analyses. The calculated difference of the neutron and proton radii exceeds 0.8 fm, confirming the thick neutron skin. The two-neutron removal spectroscopic amplitudes are calculated and used for evaluating the momentum distribution and the $β$ decay spectrum, which are sensitive to the halo structure. A fair agreement with experiment is obtained.

nucl-th↗
arXiv1993

Microscopic multicluster description of neutron-halo nuclei with a stochastic variational method

To test a multicluster approach for halo nuclei, we give a unified description for the ground states of $^6$He and $^8$He in a model comprising an $α$ cluster and single-neutron clusters. The intercluster wave function is taken a superposition of terms belonging to different arrangements, each defined by a set of Jacobi coordinates. Each term is then a superposition of products of gaussian functions of the individual Jacobi coordinates with different widths, projected to angular momenta $l=0$ or 1. To avoid excessively large dimensions and ``overcompleteness", stochastic methods were tested for selecting the gaussians spanning the basis. For $^6$He, we were able to calculate ground-state energies that are virtully exact within the subspace defined by the arrangements and $l$ values, and we found that preselected random sets of bases (with or without simulated annealing) yield excellent numerical convergence to this ``exact" value with thoroughly truncated bases. For $^8$He good energy convergence was achieved in a state space comprising three arrangements with all $l=0$, and there are indications showing that the contributions of other subspaces are likely to be small. The $^6$He and $^8$He energies are reproduced by the same effective force very well, and the matter radii obtained are similar to those of other sophisticated calculations.

nucl-th↗