arXiv subjects

Kazuyuki Ogata

Publications and source records attributed to Kazuyuki Ogata.

At least 73 records · Page 4Linked to original sources

arXiv2016

Microscopic effective reaction theory for deuteron-induced reactions

The microscopic effective reaction theory is applied to deuteron-induced reactions. A reaction model-space characterized by a $p+n+{\rm A}$ three-body model is adopted, where A is the target nucleus, and the nucleon-target potential is described by a microscopic folding model based on an effective nucleon-nucleon interaction in nuclear medium and a one-body nuclear density of A. The three-body scattering wave function in the model space is obtained with the continuum-discretized coupled-channels method (CDCC), and the eikonal reaction theory (ERT), an extension of CDCC, is applied to the calculation of neutron removal cross sections. Elastic scattering cross sections of deuteron on $^{58}$Ni and $^{208}$Pb target nuclei at several energies are compared with experimental data. The total reaction cross sections and the neutron removal cross sections at 56 MeV on 14 target nuclei are calculated and compared with experimental values.

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arXiv2016

Investigating the alpha-clustering on the surface of $^{120}$Sn via ($p$,$pα$) reaction and the validity of the factorization approximation

The $^{120}$Sn($p$,$pα$)$^{116}$Cd reaction at 392 MeV is investigated with the distorted wave impulse approximation (DWIA) framework. We show that this reaction is very peripheral mainly because of the strong absorption of $α$ by the reaction residue $^{116}$Cd, and the $α$-clustering on the nuclear surface can be probed clearly. We investigate also the validity of the so-called factorization approximation that has frequently been used so far. It is shown that the kinematics of $α$ in the nuclear interior region is significantly affected by the distortion of $^{116}$Cd, but it has no effect on the reaction observables because of the strong absorption in that region.

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arXiv2016

Determination of a dineutron correlation in Borromean nuclei via a quasi-free knockout ($p,pn$) reaction?

To discuss the dineutron correlation in the ground state, the quasi-free neutron knockout reaction on $^6$He is investigated.In the present work, the momentum distribution of the two emitted neutrons is calculated with the $α$~+~$n$~+~$n$ three-body model and a simple reaction model to assess the effects of the knockout process via the $^5$He resonance and the target dependence in the momentum distribution. A clear signature of the dineutron correlation can be obtained by choosing the kinematical condition so the process via the $^5$He resonance is excluded because the $^5$He resonance drastically changes the momentum distribution. Using the proton target is important in the quantitative discussion on the dineutron correlation by the knockout reaction. In addition to theoretical arguments, a possible experimental setup to determine the dineutron correlation via the quasi-free knockout reaction is considered.

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arXiv2016

Deuteron-nucleus total reaction cross sections up to 1 GeV

Total reaction cross sections of deuteron, $σ_d^{\rm R}$, are calculated by a microscopic three-body reaction model. The reaction model has no free adjustable parameter and applicable to reactions at various deuteron incident energies $E_d$ and with both stable and unstable nuclei. The predicted $σ_d^{\rm R}$ are consistent with those evaluated by a phenomenological optical potential for $E_d\leq 200$ MeV in which the potential has been parametrized. A simple formula of $σ_d^{\rm R}$ up to $E_d=1$ GeV, as a function of $E_d$, the target mass number $A$ and its atomic number $Z$, is given.

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arXiv2016

Applicability of the continuum-discretized coupled-channels method to the deuteron breakup at low energies

We re-examine the deuteron elastic breakup cross sections on 12C and 10Be at low incident energies, for which a serious discrepancy between the continuum-discretized coupled-channels method (CDCC) and the Faddeev-Alt-Grassberger-Sandhas theory (FAGS) was pointed out. We show the closed-channels neglected in the preceding study affect significantly the breakup cross section calculated with CDCC, resulting in good agreement with the result of FAGS.

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arXiv2016

Probing surface distributions of $α$ clusters in $^{20}$Ne via $α$-transfer reaction

Direct evidence of the $α$-cluster manifestation in bound states has not been obtained yet, although a number of experimental studies were carried out to extract the information of the clustering. In particular in conventional analyses of $α$-transfer reactions, there exist a few significant problems on reaction models, which are insufficient to qualitatively discuss the cluster structure. We aim to verify the development of the $α$-cluster structure from observables. As the first application, we plan to extract the spatial information of the cluster structure of the $^{20}$Ne nucleus in its ground state through the cross section of the $α$-transfer reaction $^{16}$O($^6$Li,~$d$)$^{20}$Ne. For the analysis of the transfer reaction, we work with the coupled-channel Born approximation (CCBA) approach, in which the breakup effect of $^6$Li is explicitly taken into account by means of the continuum-discretized coupled-channel method based on the three-body $α+ d + {}^{16}$O model. The two methods are adopted to calculate the overlap function between $^{20}$Ne and $α+ {}^{16}$O; one is the microscopic cluster model (MCM) with the generator coordinate method, and the other is the phenomenological two-body potential model (PM). We show that the CCBA calculation with the MCM wave function gives a significant improvement of the theoretical result on the angular distribution of the transfer cross section, which is consistent with the experimental data. Employing the PM, it is discussed which region of the cluster wave function is probed on the transfer cross section. It is found that the surface region of the cluster wave function is sensitive to the cross section. The present work is situated as the first step in obtaining important information to systematically investigate the cluster structure.

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arXiv2016

Consistency between the monopole strength of the Hoyle state determined by structural calculation and that extracted from reaction observables

We analyze the $α$-$^{12}$C inelastic scattering to the $0^+_2$ state of $^{12}$C, the Hoyle state, in a fully microscopic framework. With no free adjustable parameter, the inelastic cross sections at forward angles are well reproduced by the microscopic reaction calculation using the transition density of $^{12}$C obtained by the resonating group method and the nucleon-nucleon $g$ matrix interaction developed by the Melbourne group. It is thus shown that the monopole transition strength obtained by the structural calculation is consistent with that extracted from the reaction observable, suggesting no missing monopole strength of the Hoyle state.

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arXiv2015

Asymmetry of the parallel momentum distribution of (p,pN) reaction residues

The parallel momentum distribution (PMD) of the residual nuclei of the 14O(p,pn)13O and 14O(p,2p)13N reactions at 100 and 200 MeV/nucleon in inverse kinematics is investigated with the framework of the distorted wave impulse approximation. The PMD shows an asymmetric shape characterized by a steep fall-off on the high momentum side and a long-ranged tail on the low momentum side. The former is found to be due to the phase volume effect reflecting the energy and momentum conservation, and the latter is to the momentum shift of the outgoing two nucleons inside an attractive potential caused by the residual nucleus. Dependence of these effects on the nucleon separation energy of the projectile and the incident energy is also discussed.

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arXiv2015

Microscopic coupled-channel calculations of nucleus-nucleus scattering including chiral three-nucleon-force effects

We analyze $^{16}$O-$^{16}$O and $^{12}$C-$^{12}$C scattering with the microscopic coupled-channels method and investigate the coupled-channels and three-nucleon-force (3NF) effects on elastic and inelastic cross sections. In the microscopic coupled-channels calculation, the Melbourne g-matrix interaction modified according to the chiral 3NF effects is used. It is found that the coupled-channels and 3NF effects additively change both the elastic and inelastic cross sections. As a result, the coupled-channels calculation including the 3NF effects significantly improves the agreement between the theoretical results and the experimental data. The incident-energy dependence of the coupled-channels and 3NF effects is also discussed.

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arXiv2015

Four-body dynamics in 6Li elastic scattering

We analyze 6Li elastic scattering in a wide range of incident energies (Ein), assuming the n + p + alpha + target four-body model and solving the dynamics with the four-body version of the continuum-discretized coupled-channels method (CDCC). Four-body CDCC well reproduces the experimental data with no adjustable parameter for 6Li + 209Bi scattering at Ein = 24-50 MeV and 6Li + 208Pb scattering at Ein = 29-210 MeV. In the wide Ein range, 6Li breakup is significant and provides repulsive corrections to the folding potential. As an interesting property, d breakup is strongly suppressed in 6Li-breakup processes independently of Ein. We investigate what causes the d-breakup suppression.

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arXiv2015

Microscopic calculations based on chiral two- and three-nucleon forces for proton- and $^{4}$He-nucleus scattering

We investigate the effects of chiral three-nucleon force (3NF) on proton scattering at 65 MeV and $^{4}$He scattering at 72 MeV/nucleon from heavier targets, using the standard microscopic framework composed of the Brueckner-Hartree-Fock (BHF) method and the $g$-matrix folding model. For nuclear matter, the $g$ matrix is evaluated from chiral two-nucleon force (2NF) of N$^{3}$LO and chiral 3NF of NNLO by using the BHF method. Since the $g$ matrix thus obtained is numerical and nonlocal, an optimum local form is determined from the on-shell and near-on-shell components of $g$ matrix that are important for elastic scattering. For elastic scattering, the optical potentials are calculated by folding the local chiral $g$ matrix with projectile and target densities. This microscopic framework reproduces the experimental data without introducing any adjustable parameter. Chiral-3NF effects are small for proton scattering, but sizable for $^{4}$He scattering at middle angles where the data are available. Chiral 3NF, mainly in the 2$π$-exchange diagram, makes the folding potential less attractive and more absorptive for all the scattering.

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arXiv2015

Breakup and finite-range effects on the 8B(d,n)9C reaction

The astrophysical factor of $^8$B($p$,$γ$)$^9$C at zero energy, $S_{18}(0)$, is determined by a three-body coupled-channels analysis of the transfer reaction $^{8}$B($d$,$n$)$^{9}$C at 14.4 MeV/nucleon. Effects of the breakup channels of $d$ and $^9$C are investigated with the continuum-discretized coupled-channels method. It is found that, in the initial and final channels, respectively, the transfer process through the breakup states of $d$ and $^9$C, its interference with that through their ground states in particular, gives a large increase in the transfer cross section. The finite-range effects with respect to the proton-neutron relative coordinate are found to be about 20%. As a result of the present analysis, $S_{18}(0)=22 \pm 6~{\rm eV~b}$ is obtained, which is smaller than the result of the previous distorted-wave Born approximation analysis by about 51%.

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arXiv2014

Extending the Eikonal Approximation to Low Energy

E-CDCC and DEA, two eikonal-based reaction models are compared to CDCC at low energy (e.g. 20AMeV) to study their behaviour in the regime at which the eikonal approximation is supposed to fail. We confirm that these models lack the Coulomb deflection of the projectile by the target. We show that a hybrid model, built on the CDCC framework at low angular momenta and the eikonal approximation at larger angular momenta gives a perfect agreement with CDCC. An empirical shift in impact parameter can also be used reliably to simulate this missing Coulomb deflection.

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arXiv2014

Analysis of a low-energy correction to the eikonal approximation

Extensions of the eikonal approximation to low energy (20MeV/nucleon typically) are studied. The relation between the dynamical eikonal approximation (DEA) and the continuum-discretized coupled-channels method with the eikonal approximation (E-CDCC) is discussed. When Coulomb interaction is artificially turned off, DEA and E-CDCC are shown to give the same breakup cross section, within 3% error, of $^{15}$C on $^{208}$Pb at 20MeV/nucleon. When the Coulomb interaction is included, the difference is appreciable and none of these models agrees with full CDCC calculations. An empirical correction significantly reduces this difference. In addition, E-CDCC has a convergence problem. By including a quantum-mechanical correction to E-CDCC for lower partial waves between $^{15}$C and $^{208}$Pb, this problem is resolved and the result perfectly reproduces full CDCC calculations at a lower computational cost.

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arXiv2014

Extracting electric dipole breakup cross section of one-neutron halo nuclei from breakup observables

How to extract an electric dipole (E1) breakup cross section σ(E1) from one- neutron removal cross sections measured by using 12C and 208Pb targets, σ_(-1n)^C and σ_(-1n)^Pb, respectively, is discussed. It is shown that within about 5% error, σ(E1) can be obtained by subtracting Γσ_(-1n)^C from σ_(- 1n)^Pb, as assumed in preceding studies. However, for the reaction of weakly-bound projectiles, the scaling factor Γis found to be two times as large as that usually adopted. As a result, we obtain 13-20% smaller σ(E1) of 31Ne at 250 MeV/nucleon than extracted in a previous analysis of experimental data. By compiling the values of Γobtained for several projectiles, Γ=(2.30 +/- 0.41)\exp(- S_n)+(2.43 +/- 0.21) is obtained, where S_n is the neutron separation energy. The target mass number dependence of the nuclear parts of the one-neutron removal cross section and the elastic breakup cross section is also investigated.

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arXiv2013

Low lying excited states of $^{24}$O investigated by self-consistent microscopic description of proton inelastic scattering

The proton inelastic scattering of $^{24}$O($p,p'$) at 62 MeV/nucleon is described by a self-consistent microscopic calculation with the continuum particle-vibration coupling (cPVC) method. The SLy5, SkM*, and SGII parameters are adopted as an effective nucleon-nucleon interaction. For all the parameters, the cPVC calculation reproduces very well the first peak at 4.65 MeV in the $^{24}$O excitation energy spectrum as well as its angular distribution. The role of the cPVC self-energy strongly depends on the effective interactions. The higher-lying strength around 7.3 MeV is suggested to be a superposition of the $3^-$ and $4^+$ states by the results with SLy5 and SGII, whereas the SkM* calculation indicates it is a pure $3^-$ state. This difference gives a rather strong interaction dependence of the angular distribution corresponding to the higher-lying strength.

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arXiv2013

Two neutron decay from the $2_1^+$ state of $^6$He

Decay mode of the $2_1^+$ resonant state of $^6$He populated by the $^6$He breakup reaction by $^{12}$C at 240 MeV/nucleon is investigated. The continuum-discretized coupled-channels method is adopted to describe the formation of the $2_1^+$ state, whereas its decay is described by the complex-scaled solutions of the Lippmann-Schwinger equation. From analysis of invariant mass spectra with respect to the $α$-$n$ and $n$-$n$ subsystems, coexistence of two decay modes is found. One is the simultaneous decay of two neutrons correlating with each other and the other is the emission of two neutrons to the opposite directions. The latter is found to be free from the final state interaction and suggests existence of a di-neutron in the $2_1^+$ state of $^6$He.

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arXiv2012

Self-consistent microscopic description of neutron scattering by $^{16}$O based on the continuum particle-vibration coupling method

The microscopic description of neutron scattering by $^{16}$O below 30 MeV is carried out by means of the continuum particle-vibration coupling (cPVC) method with the Skyrme nucleon-nucleon ($NN$) effective interaction. In the cPVC method, a proper boundary condition on a nucleon in continuum states is imposed, which enables one to evaluate the transition matrix in a straightforward manner. Experimental data of the total and total-elastic cross sections are reproduced quite well by the cPVC method. An important feature of the result is the fragmentation of the single-particle resonance into many peaks as well as the shift of its centroid energy. Thus, some part of the fine structure of the experimental cross sections at lower energies is well described by the cPVC framework. The cPVC method based on a real $NN$ effective interaction is found to successfully explain about 85% of the reaction cross section, through explicit channel-coupling effects.

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