arXiv subjects

W. Horiuchi

Publications and source records attributed to W. Horiuchi.

84 records · Page 5Linked to original sources

arXiv2010

Green's function method for strength function in three-body continuum

Practical methods to compute dipole strengths for a three-body system by using a discretized continuum are analyzed. New techniques involving Green's function are developed, either by correcting the tail of the approximate wave function in a direct calculation of the strength function or by using a solution of a driven Schroedinger equation in a summed expression of the strength. They are compared with the complex scaling method and the Lorentz integral transform, also making use of a discretized continuum. Numerical tests are performed with a hyperscalar three-body potential in the hyperspherical-harmonics formalism. They show that the Lorentz integral transform method is less practical than the other methods because of a difficult inverse transform. These other methods provide in general comparable accuracies.

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arXiv2010

Probing the weakly-bound neutron orbit of $^{31}$Ne with total reaction and one-neutron removal cross sections

A candidate of a neutron-halo nucleus, $^{31}$Ne, contains a single neutron in the $pf$ shell. Within the Glauber and eikonal models, we analyze reactions used to study $^{31}$Ne. We show in a $^{30}$Ne+n model that the magnitudes of the total reaction and above all of the one-neutron removal cross sections of $^{31}$Ne on $^{12}$C and $^{208}$Pb targets strongly depend on the orbital angular momentum of the neutron, thereby providing us with efficient ways to determine both the spin-parity and structure of the ground state of $^{31}$Ne. Besides these inclusive observables, we also calculate energy and parallel-momentum distributions for the breakup of $^{31}$Ne, and show their strong dependence upon the orbital of the valence neutron in the bound state of $^{31}$Ne.

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arXiv2008

Phase-shift calculation using continuum-discretized states

We present a method for calculating scattering phase shifts which utilizes continuum-discretized states obtained in a bound-state type calculation. The wrong asymptotic behavior of the discretized state is remedied by means of the Green's function formalism. Test examples confirm the accuracy of the method. The $α+n$ scattering is described using realistic nucleon-nucleon potentials. The $3/2^-$ and $1/2^-$ phase shifts obtained in a single-channel calculation are too small in comparison with experiment. The $1/2^+$ phase shifts are in reasonable agreement with experiment, and gain contributions both from the tensor and central components of the nucleon-nucleon potential.

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arXiv2008

Significance and properties of internucleon correlation functions

We show that a nuclear Hamiltonian and a set of internucleon correlation functions is in a one-to-one correspondence. The correlation functions for $s$-shell nuclei interacting via the two-nucleon interaction of AV8$^\prime$ type are calculated to exhibit the importance of tensor correlations as well as short-range central correlation. The asymptotic behavior of the correlation functions is also discussed.

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arXiv2008

Elastic and total reaction cross sections of oxygen isotopes in Glauber theory

We systematically calculate the total reaction cross sections of oxygen isotopes, $^{15-24}$O, on a $^{12}$C target at high energies using the Glauber theory. The oxygen isotopes are described with Slater determinants generated from a phenomenological mean-field potential. The agreement between theory and experiment is generally good, but a sharp increase of the reaction cross sections from ^{21}O to ^{23}O remains unresolved. To examine the sensitivity of the diffraction pattern of elastic scattering to the nuclear surface, we study the differential elastic-scattering cross sections of proton-^{20,21,23}O at the incident energy of 300 MeV by calculating the full Glauber amplitude.

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arXiv2008

Inversion doublets of 3N+N cluster structure in excited states of $^4$He

Excited states of $^4$He are studied in four-body calculations with explicitly correlated Gaussian bases. All the levels below $E_{\rm x}$=26 MeV are reproduced reasonably well using realistic potentials. An analysis is made to show how the $0^+_2$ state becomes a resonance but those having almost the same structure as this state in different spin-isospin channels are not observed as resonances. The role of tensor force is stressed with a particular attention to the level spacing between the two $0^-$ states. The calculation of spectroscopic amplitudes, nucleon decay widths, and spin-dipole transition strengths demonstrates that the $0^+_2$ state and the three lowest-lying negative-parity states with $0^-$ and $2^-$ have $^3$H+$p$ and $^3$He+$n$ cluster configurations, leading to the interpretation that these negative-parity states are the inversion doublet partners of the $0^+_2$ state.

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arXiv2008

Global-Vector Representation of the Angular Motion of Few-Particle Systems II

The angular motion of a few-body system is described with global vectors which depend on the positions of the particles. The previous study using a single global vector is extended to make it possible to describe both natural and unnatural parity states. Numerical examples include three- and four-nucleon systems interacting via nucleon-nucleon potentials of AV8 type and a 3$α$ system with a nonlocal $αα$ potential. The results using the explicitly correlated Gaussian basis with the global vectors are shown to be in good agreement with those of other methods. A unique role of the unnatural parity component, caused by the tensor force, is clarified in the $0^-_1$ state of $^4$He. Two-particle correlation function is calculated in the coordinate and momentum spaces to show different characteristics of the interactions employed.

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arXiv2007

Reaction cross sections of carbon isotopes incident on a proton

We systematically study total reaction cross sections of carbon isotopes with N=6-16 on a proton target for wide range of incident energies, putting an emphasis on the difference from the case of a carbon target. The analysis includes the reaction cross sections of ^{19,20,22}C at 40 AMeV, the data of which have recently been measured at RIKEN. The Glauber theory is used to calculate the reaction cross sections. To describe the intrinsic structure of the carbon isotopes, we use a Slater determinant generated from a phenomenological mean-field potential, and construct the density distributions. To go beyond the simple mean-field model, we adopt two types of dynamical models: One is a core+n model for odd-neutron nuclei, and the other is a core+n+n model for 16C and 22C. We propose empirical formulas which are useful in predicting unknown cross sections.

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arXiv2007

Momentum distribution and correlation of two-nucleon relative motion in $^6$He and $^6$Li

The momentum distribution of relative motion between two nucleons gives information on the correlation in nuclei. The momentum distribution is calculated for both $^{6}$He and $^6$Li which are described in a three-body model of $α$+$N$+$N$. The ground state solution for the three-body Hamiltonian is obtained accurately using correlated basis functions. The momentum distribution depends on the potential model for the $N$-$N$ interaction. With use of a realistic potential, the $^6$He momentum distribution exhibits a dip around 2 fm$^{-1}$ characteristic of $S$-wave motion. In contrast to this, the $^6$Li momentum distribution is very similar to that of the deuteron; no dip appears because it is filled with the $D$-wave component arising from the tensor force.

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arXiv2006

Systematic analysis of reaction cross sections of carbon isotopes

We systematically analyze total reaction cross sections of carbon isotopes with N=6--16 on a $^{12}$C target for wide range of incident energy. The intrinsic structure of the carbon isotope is described by a Slater determinant generated from a phenomenological mean-field potential, which reasonably well reproduces the ground state properties for most of the even $N$ isotopes. We need separate studies not only for odd nuclei but also for $^{16}$C and $^{22}$C. The density of the carbon isotope is constructed by eliminating the effect of the center of mass motion. For the calculations of the cross sections, we take two schemes: one is the Glauber approximation, and the other is the eikonal model using a global optical potential. We find that both of the schemes successfully reproduce low and high incident energy data on the cross sections of $^{12}$C, $^{13}$C and $^{16}$C on $^{12}$C. The calculated reaction cross sections of $^{15}$C are found to be considerably smaller than the empirical values observed at low energy. We find a consistent parameterization of the nucleon-nucleon scattering amplitude, differently from previous ones. Finally, we predict the total reaction cross section of $^{22}$C on $^{12}$C.

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arXiv2006

$^{22}$C: $S$-Wave Two-Neutron Halo

A dripline nucleus $^{22}$C is studied in a Borromean three-body model of $^{20}$C+$n$+$n$. The valence neutrons, interacting via a realistic potential, are constrained to be orthogonal to the occupied orbits in $^{20}$C. We obtain ample results supporting that $^{22}$C is an ideal $S$-wave two-neutron halo nucleus: The ground state is bound by 390-570 keV, the root mean square neutron and proton radii are 4.0 and 2.4 fm, and the two neutrons are predominantly in $(s_{1/2})^2$ orbits. The binding mechanism of $^{22}$C is discussed. One- and two-body density distributions elucidate the halo character as well as the correlated motion of the neutrons. The reaction cross sections of $^{22}$C+$^{12}$C collisions are predicted.

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arXiv2006

Structure of and E2 transition in $^{16}$C in a $^{14}$C+n+n model

A three-body model of $^{14}$C+n+n is applied to study the energy spectrum and the hindered $E$2 transition in $^{16}$C. A realistic two-nucleon potential is used for the valence neutrons. Both spin singlet and triplet components for the neutrons are taken into account. The three-body problem with a Pauli constraint is solved in a stochastic variational method. For the n-$^{14}$C potential chosen to reproduce the properties of $^{15}$C, the low-lying energy spectrum agrees reasonably well with experiment, but the ground state is predicted to be about 1 MeV high. The calculated $B(E2$; $2_1^+ \to 0^+_1)$ value is about twice the measured value if the polarization charge of the valence neutrons is taken to be the same as that required to fit the $^{15}$C data. The correlated motion of the valence neutrons is displayed through the two-neutron density distribution.

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