九大原子核セミナー

九州大学の原子核理論と原子核実験の共同開催のセミナー

第948回九大原子核セミナー

2018年5月31日(金) 16:30〜18:00

講師: 伊藤 誠 氏 (九州大学)
演題:Evidence of an enhanced nuclear radius of the α-halo state via α + 12C inelastic scattering

場所:ウェスト1号館7階 物理会議室 (W1-A-723室)

概要:
Evidence of the enhanced nuclear radius in the Hoyle rotational state, 2_2^+ , is derived from the differential cross sections in the α+12C inelastic scattering. The prominent shrinkage is observed in the differential cross section of the 2_2^+ state in comparison to the yrast 2_1^+ state, and this shrinkage is a first evidence of the enhanced nuclear radius, which is originated from the 3α structure in the 2_2^+ state. The diffraction formula, such as Blair’s phase rule, is applied to the differential cross sections, and the present analysis predicts about 0.6 -- 1.0 fm enhancement in the nuclear radius of the 2_2^+ state in comparison to the radius of the ground state. We also show the extension of the our analysis to the production reaction of a Lambda hyper nucleus, such as 13C(K−, π−)13C. The probe of the enhanced nuclear radius in the Λ13C = 3α + Λ structure will be discussed.

q948.pdf
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第947回九大原子核セミナー

2018年4月20日(金) 16:30〜18:00

講師: Dalibor Skoupil 氏 (九州大学)
演題:Electromagnetic Production of Hyperons

場所:ウェスト1号館7階 物理会議室 (W1-A-723室)

概要:
The aim of this presentation is to provide an overview of the strangeness photo- and electroproduction reaction, especially K+ Lambda photo- and electroproduction off proton, and report on recent progress in this field. The kaon photoproduction on the proton is studied either in the resonance region, using an isobar model, or in the resonance region and beyond, exploiting a hybrid Regge-plus-resonace (RPR) framework. The higher-spin nucleon, spin-3/2 and spin-5/2, and hyperon, spin-3/2, resonances have been included in the model utilizing the consistent formalism by Pascalutsa and they were found to play an important role in data description. A further upgrade of our model was accomplished by implementing energy-dependent widths of nucleon resonances, which leads to a different choice of hadron form factor with much softer values of cutoff parameter for the resonant part. For a reliable description of electroproduction, the necessity of including longitudinal couplings of nucleon resonances to virtual photons was revealed. The free parameters of the models were fitted either solely to photoproduction data or to both photo- and electroproduction data from many collaborations, resulting in BS1 isobar model and RPR fit for photoproduction and a BS3 version of isobar model eligible also for electroproduction description. All models provide a reasonable overall description of the data in the kinematic regions where the free parameters were adjusted. Even though the kaon photoproduction takes place in the third-resonance region with many resonant states, the total number of included resonances, 15, 16, and 10 in the BS1, BS3, and RPR models, respectively, is quite moderate and it is comparable with amounts of resonances in other models. Moreover, the majority of nucleon resonances chosen in this analysis coincide with those selected in the Bayesian analysis with the RPR model as the states contributing to this process with the highest probability.

q947.pdf
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第944回九大原子核セミナー

2018年3月1日(木) 16:30〜18:00

講師:Jirina Stone 氏(Tennessee大学)

演題:Superheavy nuclei in the Quark-Meson Coupling model

場所:ウェスト1号館7階 物理会議室 (W1-A-723室)

概要:
The fundamental problem of low energy nuclear structure is the understanding the change of the free nucleon-nucleon force in the nuclear medium. Commonly used forces of the Skyrme or Gogny type, with their empirical medium density dependence, cannot be determined uniquely. Hundreds of such forces have been constructed, fitting their numerous correlated parameters to selected experimental data. We report a single, four-parameter form of the density dependent effective nucleon-nucleon force based on modification of the nucleon structure in-medium on the quark level, which represents a new paradigm for nuclear physics. The model yields results for the ground-state binding energies, electromagnetic properties and shapes of even-even nuclei, from the lightest to superheavy, in agreement with experiment within less than a few percent [1].
I will discuss the latest results obtained for binding energies, deformations and single-particle energies of even-even nuclei in the region of 100 < Z < 110 and their comparison with available experimental data. Extension of the model to nuclei with the atomic number up to 120, predicted shell closures and attempts to identify an island of stability in the superheavy region will be reported [2].

[1] J.R.Stone, P.A.M. Guichon, P.-G. Reinhard and A.W. Thomas,
Phys.Rev.Lett. 116, 092501 (2016)
[2] J.R.Stone, P.A.M.Guichon and A.W.Thomas, https://arxiv.org/abs/1706.01153v1

q944.pdf
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第943回九大原子核セミナー

2018年2月6日(火) 16:30〜18:00

講師:佐川弘幸 氏(会津大学/理研)

演題:IS and IV pairing correlations and Spin-Isospin Response

場所:ウェスト1号館7階 物理会議室 (W1-A-723室)

概要:
Pairing correlations are one of the most important effects in nuclear structure and reactions.Spin-singlet isovector pairing correlations have been discussed from late 1950s and the spin-singlet superfluidity is well established in several observations such as the energy spectra of even-even nuclei and the moment of inertia of deformed nuclei. It is also known that the spin-triplet isoscalar pairing interaction is much stronger than the isovector one in the nuclear matter calculations. The existence of deuteron certainly proves the strong spin-triplet isoscalar correlations. I will discuss in this talk how we can nd out the effect of isoscalar pairing correlations in spin-isospin response of N=Z nuclei, especially magnetic dipole transitions and Gamow-Teller transitions.

q943.pdf
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第942回九大原子核セミナー

2018年1月22日(月) 16:30〜18:00

講師:池田陽一氏(阪大RCNP)

演題:"The Tetraquark Candidate Zc(3900) from coupled-channel scat-
tering on the lattice"

場所:ウェスト1号館7階 物理会議室 (W1-A-723室)

概要:
The structure of the tetraquark candidate Zc(3900), which was experimentally reported in e+e- collisions, is studied by the s-wave meson-meson coupled-channel scattering on the lattice.The s-wave interactions among the πJ/ψ, ρηc and DD* channels are derived from (2+1)-flavor dynamical QCD simulations at mπ = 410-700 MeV. It is found that the interactions are dominated by the off-diagonal πJ/ψ-DD* and ρηc-DD* couplings. With the interactions obtained, the s-wave two-body amplitudes and the pole position in the πJ/ψ-ρηc-DD* coupled-channel scattering are calculated. The results show that the Zc(3900) is not a conventional resonance but a threshold cusp. A semiphenomenological analysis with the coupled-channel interaction to the experimentally observed decay mode is also presented to con rm the conclusion.

q942.pdf
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