肥山ストレンジネス核物理研究室

Links to Seminars held in RIKEN

- Seminars of RIKEN : 日本語のセミナー and English seminars
- Seminars of Nishina Center: 日本語/English
- Seminars of iTHES/iTHEMS (English only)

11 Oct.

13:30

RIKEN Main Research Building, room 224&226

Michele Viviani (INFN Pisa & Department of Physics, University of Pisa)

Theoretical study of three and four neutron resonances

Recently, the interest on establishing the existence of low energy three and four neutron resonances has been renewed. The possible existence of a four neutron resonance has been recently reported experimentally, but different theoretical groups find conflicting solutions on that problem. In this talk, this issue is studied solving the 3n→3n and 4n→4n scattering problems using the adiabatic Hyperspherical Harmonic approach. The preliminary results of this investigation will be shown and discussed.

7/25

11:00

RIKEN Main Research Building, room 224&226

Yuki Kamiya (Yukawa Institute for Theoretical Physics, Kyoto University)

Model-independent determination of structure of exotic hadrons with the scattering amplitude

Understanding of the internal structure of exotic hadrons is an important topic of the current hadron physics. Particularly in recent years, precise data on the hadron scattering have been accumulated from the experimental analysis, and it is becoming possible to extract detailed information on the scattering amplitude. This enables us to study the hadron structure from the properties of the scattering amplitude. In this seminar, the model-independent approaches to study the hadron structure from the scattering amplitude are discussed. In the first part, the weak-binding relation between the experimental observables and compositeness, defined as the probability of finding the composite component, is introduced [1, 2]. While the compositeness is in general model-dependent quantity, this can be calculated in a model-independent manner using the experimental observables when the hadron is weakly-binding s-wave state. Here, I mainly explain the reasoning of small model dependence of the compositeness in the weak-binding limit. In the second part, we see the qualitative method using the position of the Castillejo-Dalitz-Dyson (CDD) zero defined as the zero of the amplitude [3]. For the eigenstate that originates in the hidden channel, the existence of the CDD zero close to the pole is indicated by the topological nature of the phase of the amplitude. At the end of each part, the applications to Lambda(1405) baryon are discussed. [1] S. Weinberg, Phys. Rev. 137, B672 (1965). [2] Y. Kamiya and T. Hyodo, Phys. Rev. C 93, 035203 (2016), Y. Kamiya and T. Hyodo, Prog. Theor. Exp. Phys. (2017) 023D02. [3] Y. Kamiya and T. Hyodo, Phys. Rev. D 97, 054019 (2018).

6/20

15:00

RIKEN Main Research Building, room 435&437

Nodoka Yamanaka (Institut de Physique Nucléaire Orsay (IPN Orsay))

The AFTER project, and the gluon and charm content of the deuteron

Fixed-target experiments using the high energy beam of the LHC can unveil various aspects of quantum chromodynamics (QCD) thanks to the ALICE and LHCb detectors, the high luminosity typical of high energy accelerators, and the versatility of the target with the possibility to polarize it. One of the most important topics to be studied is the nucleon structure when the constituents (partons) have a high momentum fraction. In the first part of this seminar, we will present the experimental project of A Fixed Target ExpeRiment (AFTER@LHC) [1], with an emphasis on the precise determination of the parton distribution functions (PDFs) of nucleons and nuclei. In the second part, we will report on the gluon and charm PDFs of the deuteron using light-front quantization together with the impulse approximation [2]. We use a nuclear wave function obtained by solving the nonrelativistic Schrödinger equation using the Gaussian expansion method [3] with the realistic Argonne v18 nuclear force; it is then convoluted with the proton PDF. As a result, we found that the gluon distribution in the deuteron (per nucleon) is smaller than that of the proton by a few percent close to x = 0.4, whereas it is enhanced at x larger than 0.6. We will discuss the applicability of our computation and will comment on how to extend it to x as large as two. We will also present the charm distribution of the deuteron within the same approach by considering perturbatively and non-perturbatively (intrinsic) generated charm inside the deuteron. In particular, we note that the intrinsic charm content in the deuteron may be enhanced for 6-quark configurations. [1] S. J. Brodsky, F. Fleuret, C. Hadjidakis, and J.-P. Lansberg, Phys. Rep. 522, 239 (2013). [2] S. J. Brodsky, K.Y.J. Chiu, J.P. Lansberg, NY, arXiv:1805.03173 [hep-ph]. [3] E. Hiyama, Y. Kino, and M. Kamimura, Prog. Part. Nucl. Phys. 51, 223 (2003).

6/18

13:30

RIKEN Main Research Building, room 224&226

Yusuke Namekawa (Institute of Physics, University of Tsukuba)

Successful prediction to charmed single hadrons and attempt on two-hadron by lattice QCD

I will present our results of charmed hadrons, with emphasis on our successful prediction to the doubly charmed baryon Ξ_{cc}. I also explain our new attempt on two-hadron interaction by lattice QCD.

5/17

13:30

RIKEN Main Research Building, room 224&226

Yoshiko Kanada-En'yo (Department of Physics, Kyoto University)

Isoscalar monopole and dipole excitations in light nuclei

The low-energy dipole excitations in neutron-rich nuclei are attracting a great interest in physics of unstable nuclei. A particular attention is paid on isoscalar and isovector natures of dipole excitations. We studied dipole excitations in Be isotopes with an extended version of the antisymmetrized molecular dynamics, which are designed to describe 1p-1h excitations and large amplitude cluster modes. Two dipole modes were obtained in the low-energy dipole excitations in 10Be. In this talk, I will briefly overview our recent researches on nuclear clustering, and then discuss the dipole excitations in light nuclei.

2/21

14:30

RIKEN Main Research Building, room 224&226

Michio Kohno (Research Center for Nuclear Physics, Osaka University)

Hyperons in nuclear matter from YN and YNN interactions in ChEFT and hyperon puzzle

In ordinary nuclei, chiral NN and NNN interactions in chiral effective field theory (ChEFT) are now standard for ab initio studies. The description of baryon-baryon interactions in the strangeness sector has also been developed. After a brief introduction to the construction of baryon-baryon interactions in ChEFT, hyperon single-particle potentials calculated in nuclear matter with NLO hyperon-nucleon (YN) and NNLO hyperon-nucleon-nucleon (YNN) interactions parametrized in ChEFT are presented. The NLO YN interactions bear strong lambda-sigma coupling. The interesting result is that the lambda potential becomes shallower beyond the normal density. Together with the repulsion from the YNN interactions, the ChEFT description provides the possibility to solve the hyperon puzzle without introducing ad hoc assumptions.

2/20

16:00

RIKEN Main Research Building, room 224&226

M. Tachikawa (Graduate School of Nanobioscience, Yokohama City University)

Ab initio calculation for positronic compounds

We have extended the conventional ab initio methods, such as molecular orbital and quantum Monte Carlo methods, to the multi-component systems, which composed of electrons, a positron, and nuclei. We have carried out the accurate calculation of positron affinity and pair annihilation rate for positronic compounds by using these multi-component methods including vibrational effect, and found that these values are in reasonable agreement with the corresponding experimental ones. [1-4] The positronic orbital is much more delocalized than the highest occupied electronic orbital, and the correlation between positron affinity and both permanent dipole moment and dipole-polarizability is clearly shown.

[1] M. Tachikawa, Y. Kita, and R. J. Buenker: Phys. Chem. Chem. Phys. 13 (2011) 2701.

[2] M. Tachikawa, Y. Kita, and R. J. Buenker: New J. Phys. 14 (2012) 035004.

[3] Y. Yamada, Y. Kita, M. Tachikawa: Phys. Rev. A 89 (2014) 062711.

[4] K. Suzuki, T. Takayanagi, Y. Kita, M. Tachikawa, and T. Oyamada: Comp. Theo. Chem. 1123 (2018) 135.

9/15

15:00

RIKEN Main Research Building, room 224&226

Hyeon-Deuk Kim (Kyoto University)

Quantum Molecular Dynamics Simulation Method for Hydrogen Molecules -From a Small Molecule to Condensed Phases-

Nuclear quantum effects of hydrogen nuclei such as zero-point energy and nuclear delocalization significantly influence dynamical and structural properties of condensed hydrogen systems. I will report the first computational study on real-time dynamics of hydrogen molecular liquids, solids, and supercooled liquids exhibiting strong nuclear quantum effects which have been hardly accessible by use of previous computational and theoretical methods like density functional theory and semiquantum molecular dynamics simulations with path integrals. [1-6] All the physical insights and information we obtained will provide a milestone for identifying and characterizing various unknown hydrogen phases, which will open a new avenue of hydrogen material research.

[1] K. Abe and K. Hyeon-Deuk, J. Phys. Chem. Lett., 8, 3595 (2017)

[2] K. Hyeon-Deuk, and K. Ando, Phys. Chem. Chem. Phys. (Communication), 18, 2314 (2016)

[3] K. Hyeon-Deuk, and K. Ando, J. Chem. Phys. (Communication), 143, 171102 (2015)

[4] K. Hyeon-Deuk, and K. Ando, Phys. Rev. B, 90, 165132 (2014)

[5] K. Hyeon-Deuk, and K. Ando, J. Chem. Phys. (Communication), 140, 171101 (2014)

[6] K. Hyeon-Deuk, and K. Ando, Chem. Phys. Lett., 532, 124 (2012)

7/5

15:00

RIKEN Main Research Building, room 224&226

Kenji Sasaki (YITP, Kyoto University)

Lattice QCD study on baryon-baryon interactions

The baryon-baryon (BB) interaction is one of the central topics in hadron and nuclear physics. Especially for the strangeness sector, in spite of lack of experimental data, detailed properties of it is required to understand the hypernuclear structures and deep inside of neutron stars. We investigate BB interactions via the time-dependent HAL QCD method which enables us to derive potentials from Nambu-Bethe-Salpeter (NBS) wave function simulated on the lattice. We report the latest results of BB potentials and their scattering observables especially focusing on the strangeness S=-2 sector. We also discuss the possibility of H-dibaryon state through the Lambda-Lambda and N-Xi scatterings.

7/5

13:30

RIKEN Main Research Building, room 224&226

Takaya Miyamoto (YITP, Kyoto University)

Lambda_c N interaction from lattice QCD and its application to Lambda_c hypernuclei

We study the Lambda_c - nucleon interaction faithful to S-matrix in QCD on the basis of the HAL QCD method. In HAL QCD method, Nambu-Bethe-Salpeter wave functions are calculated on the lattice, and potentials are extracted form them. I will present our results on the 1S0 and 3S1 Lambda_c - nucleon potentials and scattering observables such as phase shifts. The scattering observables show that the Lambda_c - nucleon interaction is attractive and its spin dependence is weak. Using the extracted potentials, we also examine possible Lambda_c nuclei by constructing a single-folding potential, which can be studied at J-PARC and FAIR in the future.

6/16

15:00

RIKEN Main Research Building, room 224&226

Mitsunori Fukuda (Osaka University)

Study of surface structure of nuclei via reaction cross sections

We have been developing a method to deduce proton-, neutron-, and nucleon-density distributions in a nucleus via the reaction cross section that stands for a possibility of nuclear collision. Using this prescription, we can now discuss halo- and skin-structures, or nuclear deformations based on the experimental reaction cross section data. In this talk, I would like to show recent results of experiments at NIRS-HIMAC* and RIKEN. Especially, the latest preliminary result from the experiment carried out at RIBF last autumn on Ca and Ni isotopes will be introduced to discuss neutron-skin thickness and the equation of state for asymmetric nuclear matter.

5/29

13:30

RIKEN Main Research Building, room 224&226

Yudai Suwa (YITP, Kyoto University)

Formation of Neutron Stars

A core-collapse supernova is a generation site of a neutron star as well as one of the largest explosions in the universe. In this talk, I will show our recent results of supernova simulations with multi-dimensional neutrino-radiation hydrodynamics, especially focusing on neutron star formations.

4/18

15:00

RIKEN Main Research Building, room 224

Ulugbek Yakhshiev (Inha University)

Topological models and their applications

In this talk some examples of the applications of instantons and skyrmions in describing the properties of strongly interacting systems will be discussed. In particular, first we discuss the contributions of nonperturbative effects in the heavy quark sector starting from the instanton induces quark-antiquark potential. The second, we start from the effective skyrmion-skyrmion interactions in a many body systems and discuss the properties of the many-nucleonic systems.

4/18

13:30

RIKEN Main Research Building, room 224

Hyun-Chul Kim (Inha University)

Heavy Baryons and excited baryons in the pion mean fields

An ordinary heavy baryon consists of one heavy quark and two light quarks. In the present seminar, we review a recent work on the mass splitting of the lowest-lying heavy baryons, based on the chiral quark-soliton model. The dynamical variables were fixed in the light-baryon sector, the experimental data being used. The results were in remarkable agreement with the experimental data. We also predict the mass of the Omega_b. Within the same framework, we also analyze recent experimental results for excited Omega_c from the LHCb experiment. We suggest possible scenarios on them. As a second part of the talk, we will discuss a recent study on excited baryons, based on the extended chiral quark-soliton model. Since the confinement plays an essential role in describing the excited baryons, we consider the confining background field in addition to the pion mean field. To avoid the divergence in the quark level, we chop off the linearly-rising confining field at a certain value that is comparable to the quark mass. We discuss the mass spectra of the first excited baryons. We also discuss the theoretical puzzles on the mass ordering of N*(1440) and N*(1535) as well as N*(1535) and N*(1520).

3/28

15:00

RIKEN main Research Building, room 224

Rimantas Lazauskas (Université de Strasbourg, Flance)

On the possible existence of 4n resonances

I will discuss about the possibility for a four neutron system to posses a narrow resonance as suggested by a recent experimental result in RIKEN. Before discussing my own development, a short overview of the experimental and theoretical results concerning pure neutron systems will be presented.

Since any sensitive modification of the nucleon-nucleon (NN) potentials or on the leading contributions of the three-nucelon (NNN) forces affect strongly the nuclear chart, in our recent work we have introduced a phenomenological T = 3/2 three neutron force, in addition to a realistic NN interaction, as an artefact to accommodate a 4n nearthreshold states. We inquired what would be the strength of such a 3n force in order to generate a resonance compatible with the experimental findings. The reliability of the resulting three-neutron force in the T = 3/2 channel is examined, by analyzing its consistency with the low-lying T = 1 states of 4H, 4He and 4Li and the 3H + n scattering. Two independent configuration space methods are used in solving the four-body problem: the Gaussian expansion method to solve the Schrodinger equation and the Lagrangemesh technique applied to solve the Fadeev-Yakubowsky equation. The boundary conditions related to the four-body problem in the continuum are implemented by using the complex scaling method and the position of the 4n resonances in the complex energy-plane are determined.

3/27

13:30

RIKEN main Research Building, room 224

Rimantas Lazauskas (Université de Strasbourg, Flance)

Some developments in few-particle scattering problem based on complex-scaling method

The solution of the scattering problem in configuration space is a very difficult task both from formal (theoretical) as well as from computational points of view. The principal difficulties are related with the complex structure of the systems wave function in the asymptotes, being result of either presence of multiple scattering channels or the systems breakup into three or more clusters. One is obliged to seek for the exact methods enabling to treat the multiparticle scattering problem by avoiding the explicit treatment of the systems wave-function at the boundaries.

Complex-scaling method, proposed in the late sixties by Nuttal and Cohen, offers very accurate and elegant formalism to treat diverse scattering problems for short range potentials. Within the last few-years I have applied this method in handling very different scattering problems: 2-body collisions including Coulomb interaction, Optical potentials; scattering including the 3-body break-up for real and Optical short-ranged interactions; 3-body and 4-body scattering for the systems, where two-particles (clusters) are charged; 3-body break-up amplitude for n-d as well as p-d scattering. Finally, I have demonstrated that the conventional smooth complex scaling technique might be also used in describing collisions in pure Coulombic 3-body systems. These recent achievements will be overviewed and discussed.

11/11

13:00

RIKEN main Research Building, room 124&126

Francisco Miguel MARQUÉS MORENO (LPC (ENSICAEN), France)

The neutron as a building block of nuclei

Neutrons decay into a proton after several minutes, and they can only escape their fate inside nuclei with the help of other protons. Do they really need protons to survive? Experimental programs try to provide a final answer to this question since the 1960s, but forming a nucleus with neutrons only is not an easy task, even theoretically! We will pass in review the different techniques that have been used, discuss a few key issues about the subject of neutral nuclei, and describe the present and future plans that should answer this question at RIKEN.

11/07

14:00

RIKEN main Research Building, room 213

Emiko Hiyama (RIKEN, Japan)

Structure of the four-body tetra neutron

10/03

13:30

RIKEN main Research Building, room 424&426

Roman Skibinski (Jagiellonian University, Poland)

Recently developed two-nucleon interactions applied to three-nucleon systems

In recent years the family of nucleon-nucleon interactions has been expanded by new models arising from different assumptions and motivations. In this talk I will focus on such forces as the improved chiral interaction of the Bochum-Bonn group, the JISP16 force and low-momentum interaction arising from the CD-Bonn force via the unitary transformation. While all models describe two-nucleon systems very well, their behaviour changes when applied to three-nucleon reactions. I will briefly overview applications of this forces to elastic nucleon-deuteron scattering and/or weak muon capture processes at energies below the pion production threshold.

08/01

13:30

RIKEN main Research Building, room 424&426

Qiang Zhao (Institute of High Energy Physics, Chinese Academy of Sciences)

Understanding the shortened lifetime of hypertriton

We study the mechanism for the hypertriton hadronic weak decay and provide an explanation for its significantly shortened lifetime which was observed recently by GSI, ALICE and STAR.

06/15

13:30

RIKEN main Research Building, room 213

Jirina Stone (University of Tennessee)

Low energy nuclear structure modeling; Can it be improved?

Enormous effort of generations of physicists has been devoted to understanding low energy nuclear structure since the discovery of the atomic nucleus in 1911. Properties of nuclei in their ground state, including their mass, building energy and shape provide a vital input to many areas of sub-atomic physics as well as astrophysics and cosmology. Low energy excited states are equally important for understanding nuclear dynamics. Yet, no consensun exis as to what is the best path to a theory, which would not only consistently reproduce a wide variety of experimental data but also have enough predictive power to yield credible predictions in area where data are still missing. In this talk I will give a basic outline of some of the main obstacles preventing us building such a theory. These include the change between the nucleon-nucleon force in free space and in nuclear environment, the saturation property of the nuclear force and effects of the sub-nucleon (quark) structure of the nucleon. Selected classes of nuclear models, shell models, mean field models, microscopic-microscopic and ab-initio models, will be discussed with emphasis on their regions of applicability. Finally, suggestions will be made for, at least partial, progress that can be made with the quark-meson coupling model, as reported in the recent publication.

05/20

13:00

RIKEN main Research Building, room 424&426

Shin Watanabe (RIKEN)

Dynamic properties of 6Li elastic scattering

We investigate four-body breakup dynamics of 6Li elastic scattering on heavy targets (n+p+α+T; T=target). Since the n+p subsystem of 6Li has a bound state as deuteron (d), there exist not only four-body breakup processes (6Li+T→n+p+α+T) but also three-body breakup processes (6Li+T→d+α+T). This makes reaction dynamics more complex in 6Li scattering than in scattering of Borromean systems such as 6He (n+n+α+T). In order to take into account both the breakup processes explicitly, 6Li is constructed by the Gaussian expansion method and the scattering process is then described with the four-body version of continuum-discretized coupled-channels method (four-body CDCC). Four-body CDCC reproduces measured elastic cross sections without introducing any adjustable parameter. In this seminar, we will discuss which of four- and three-body breakup processes is favored in 6Li scattering and clarify the dynamic properties of 6Li scattering.

05/20

11:00

RIKEN main Research Building, room 424&426

Tingting Sun (Zhengzhou University, Peking University)

Relativistic mean field approaches for Xi^- hypernuclei and current experimental data

Motivated by the recently observed hypernucleus (Kiso event) Xi15C (14N+Xi^-), we identify the state of this system theoretically within the framework of the relativistic-mean-field model. The XiN interactions are constructed to reproduce the two possibly observed \Xi^- removal energies, 4.38\pm 0.25 MeV or 1.11\pm 0.25 MeV. The preferred interpretation of the event is 14N(g.s.)+Xi^-(1p), which is consistent with previous data on the hypernucleus Xi12Be (11B+Xi^-).

01/06

16:00

RIKEN main building, room 424

Ulugbek Yakhshiev (Inha University)

From nucleons to nucleonic systems (Chiral soliton approach)

We discuss the structure of the nucleon in free space and its structure changes in nuclear environment in the framework of in-medium modified chiral soliton model. The influence of surrounding nuclear environment to the in-medium nucleon properties is taken into account by means of the pion-nucleus optic potential in the mesonic sector. The parameters of the optic potential are related to the pionic atoms data at low densities and to the nuclear matter matter properties at the saturation density. Then the properties of symmetric and asymmetric nuclear matter are discussed. Further, considering the extrapolations to extreme high densities, the structure and properties of neutron stars are also discussed.

12/18

14:00

RIKEN main building, room 224

Kenta Miyahara (Kyoto University)

Weak decays of charmed baryons for the study of strange baryon resonances

Recently, three-body decays of the ground state charmed baryons like Lambda_c and Xi_c have been measured by Belle and BESIII collaborations. These decays lead to the analysis of interesting baryon resonances with strangeness such as Lambda(1405) and Xi(1690) through the final state interaction of the meson-baryon pair. In this work, we study the weak decay processes theoretically, and find that these are ideal to analyze the properties of resonances. For instance, these decays can filter the isospin of the meson-baryon pair and provide clear resonance signal compared with other production reactions. With the decay processes, we calculate the spectra of Lambda and Xi resonances and conclude that these decays are quite useful to clarify the nature of the baryon resonances with strangeness S=-1 and -2.

11/20

14:00

RIKEN main building, room 224

Takuma Yamashita (Tohoku University)

Weakly binding system of positronic alkali atom: relativistic effects and resonance states

Positron (e^{+}), an anti-particle of an electron, can be bound to some kinds of atoms and forms positronic atoms. Since the positron has the same but an opposite sign of charge, the positron lies far away from the nucleus by Coulombic repulsion. A positron and an electron form a hydrogen-like bound state which is called a positronium (Ps). Because of the same mass as an electron, the wavefunction of the positron spreads widely. Positron can be an alternative and a unique probe to electronic states of atoms/molecules by analyzing annihilation gamma rays. Recently, a low energy and high resolution positron beam has been developed, and the search for resonance states of positronic noble gas atoms is becoming possible [1]. Since the positronic atoms are expected to show many different faces from ordinary atoms, many theoretical and experimental attempts have been made to open a new aspect of atomic physics. Positronic alkali atoms (APs^{+}) have a minimum necessary to describe the positronic and electronic states of positronic atoms and have been the best testing grounds. We can regard the alkali atom (A) as a two-body model consisting of a valence electron and residual closed-shell ion core (A^{+}). Both positron-valence electron active correlation and polarization of the ion core/atom can be described effectively. Since the ionization energy of an alkali atom is smaller than that of a Ps, the structure of the loosely bound state of APs^{+}shows Ps cloud which exists as Ps halo [2]. In this work, we precisely calculate bound and resonance states of LiPs^{+}, NaPs^{+}, KPs^{+}, RbPs^{+}and CsPs^{+}as a three-body system {A^{+}, e^{-}, e^{+}} with a Gaussian Expansion Method, and find unique and exotic features of positronic alkali atoms. Relativistic effects based on the Breit-Pauli interactions to loosely bound states of LiPs^{+}and NaPs^{+}are investigated [3] by comparing with normal atoms. Structures and mechanisms of resonance states caused by weak long-range forces are also investigated. [1] J. R. Machacek, R. Boadle, S. J. Buckman, and J. P. Sullivan, Phys. Rev. Lett. 86, 064702 (2012). [2] J. Mitroy, Phys. Rev. Lett. 94, 033402 (2005). [3] T. Yamashita, and Y. Kino, J. Phys. Conf. Ser., 635, 052086 (2015).

11/12

14:00

RIKEN main building, room 224

Doerte Blume (Washington State University)

The helium Efimov trimer and larger bosonic droplets

The quantum mechanical three-body problem has been studied extensively for about a century. The helium atom (two electrons and a nuclues) and the molecular hydrogen ion (two protons and one electron) are textbook examples that illustrate the organization of the periodic table and molecular binding mechanisms, respectively. In 1970 Vitaly Efimov predicted a rather different and counterintuive quantum mechanical three-body binding mechanism that leads to an infinite series of stable three-body states of enormous spatial extents. These Efimov states are predicted to exist for short-range interactions like the van der Waals force between atoms or the strong force between nucleons. When the potential becomes so shallow that the last two-body bound state is at the verge of becoming unbound or is unbound, then three particles stick together to form Efimov states. This talk will review recent theoretical and experimental advances in this field. The observation of the helium trimer (three neutral helium atoms) Efimov state and extensions of the Efimov scenario to four- and higher-body systems will be discussed.

10/19

13:00

RIKEN main building, room 424

田中拓男 (理化学研究所 田中メタマテリアル研究室)

光メタマテリアル

「メタマテリアル」は，電磁波の波長より小さな構造を用いて物質の電磁気学特性を操作した人工物質である．メタマテリアルは，マイクロ波から光波まで幅広い周波数領域で研究されているが，我々は特に光の領域で動作する「光メタマテリアル」の実現とその応用展開を目指して研究を進めている．これまで我々は，この光メタマテリアルを作るために必要な加工技術を中心に，レーザーを用いたトップダウン的な手法や，DNAや磁場を用いたボトムアップ的な手段，さらに最近では，トップダウンとボトムアップを融合させた新しい手法を開発・提案してきた．講演では，これらの内容とともに，メタマテリアルのサイエンスとテクノロジーについて紹介する．

10/19

11:00

RIKEN main building, room 424

Carlo Barbieri (University of Surrey, UK)

Medium-mass isotopes from three-nucleon chiral interactions and Lattice QCD forces

The seminar will review two related developments in the ab-initio study of medium-mass exotic nuclei. The self-consistent Green’s function theory method is used to learn about the characteristics of single nucleon correlations along several full spectroscopic chains. In the first case, chiral EFT interactions have been used to obtain the nuclear spectral function of the oxygen isotopes. This confirmed from the ab-initio perspective the mechanism by which three nucleon forces generate the anomalous dripline at O24 and also affect nearby fluorine isotopes. We will also discuss implication of 3NFs for the Ca chain and its neighbours. Very neutron rich Ca and K isotopes have recently been measured and suggest the necessity for improved chiral interactions. In the second part, we will discuss the structure of closed shell isotopes as generated by nuclear forces from Lattice QCD simulations. For pion mass of 470 MeV (now getting closer to the physics limit) 4He and 40Ca are finally bound. However, the 16O could be still unstable under breakup onto four alpha particles.

7/27

14:00

RIKEN main building, room 224

Petr Vesely (Nuclear Physics Institute, Czech)

Hypernuclear Spectra within Mean Field and Beyond Mean Field Approach

In the first part of talk I will introduce the calculations of (ordinary) nuclei based on the self-consistent HFB method, solved with the realistic NN interactions, and subsequent Equation of Motion Phonon Model (EMPM). The EMPM model is used for the calculations of the excitation spectra within multi particle-hole configuration space. Such configurations are important to incorporate the beyond mean field correlations into the description of nuclear spectra. In the second part of the talk I will speak about the modification of this model which allows to describe the spectra of medium and heavy hypernuclei.

7/22

14:30

RIKEN main building, room 424

Kei Yamamoto (山本恵) (KEK)

Probing high scale SUSY in low energy FCNC

Heavy flavor physics has played an essential role in testing the CKM paradigm of the Standard Model and in searching for new physics. CP violation and rare decays of K and B meson and EDM can be good probe for new physics such as supersymmetry. In our work, taking account of the recent LHC results for the Higgs discovery and the SUSY searches we consider the high-scale SUSY scenario in the framework of the non-minimal flavor violation. We discuss the effect of the high scale SUSY on FCNC of K, B0 and Bs mesons. References: M. Tanimoto and K. Yamamoto, "Sensitivity of High-Scale SUSY in Low Energy Hadronic FCNC”, Symmetry 7 (2015) 689 [arXiv:1506.01850 [hep-ph]]. M.Tanimoto and K.Yamamoto, "Probing the high scale SUSY in CP violations of K, B0 and Bs mesons", Phys. Lett. B 735 (2014) 426 [arXiv:1404.0520 [hep-ph]].

6/22

15:00

RIKEN main building, room 424

Tomoya Murata (村田知也) (Osaka University)

Neutrino induced ^{4}He break up reaction

The neutrino-nucleus reactions play an important role for the heating and cooling mechanism in the core collapse supernova explosion. In addition to neutrons, protons and one representative nuclei line iron,^{4}He has been considered in the equation of state of supernovae. In ref. [1], light nuclei such as deuteron, triton and 3He are taken into account.^{4}He has been considered as a significant component and the importance of neutrino-4He reactions has been studied in the accelerating shockwave [2] and nucleosynthesis [3]. The neutrino-^{4}He reaction cross sections are evaluated in shell-model approach[4] and an approach using Lorentz Integral Transformation method [5]. In this presentation, we will report on our analysis of cross sections and temperature averaged cross sections for CC and NC (anti-)neutrino induced^{4}He break up reactions: ν_{e}+^{4}He → e^{-}+ X(A=4, Z=3) \bar{ν_{e}} +^{4}He → e^{-}+ X(A=4, Z=1) ν_{e}/ \bar{ν_{e}} +^{4}He → ν_{e}/ \bar{ν_{e}} + X(A=4, Z=2). For this analysis, we have employed the spin-dipole and dipole strength functions of^{4}He calculated in the Complex Scaling Method (CSM) [6]. Comparison with the previous works will be discussed. [1] K. Sumiyoshi and G. Ropke, Phys. Rev. C77, 055804 (2008). [2] W. C. Haxton, Phys. Rev. Lett. 60, 1999 (1988). [3] G. M. Fuller and B. S. Meyer, Astrophys. J. 453, 792 (1995). [4] T. Suzuki, S. Chiba, T. Yoshida, T. Kajino and T. Otsuka, Phys. Rev. C74, 034307 (2006). [5] D. Gazit and N. Barnea, Phys. Rev. Lett. 98, 192501 (2007). [6] W. Horiuchi and Y. Suzuki, Phys. Rev. C87, 034001 (2013).

11/14

15:00

RIKEN main building, room 433

Hyun-Chul Kim (Inha University)

The charge and spin structure of the nucleon and the pion

In the present talk, we review series of recent works on the charge and spin structure of the nucleon and the pion. We emphasize the new concept of the transverse charge and spin densities of hadrons. The corresponding results are discussed.

09/29

15:00

RIKEN main building, room 124-126

Sho Nagao(永尾翔) (Tohoku University)

Spectroscopy of electro-produced hypernuclei at Mainz Microtron

See here (PDF file).

08/01

13:30

東京工業大学大岡山キャンパス本館第二会議室（345号室） (Hadron Spectroscopy Cafe)

中村真 (中央大学)

AdS/CFT対応を用いた非平衡統計物理学への挑戦

多体系の物理学は特定の分科を超えた物理学共通の研究課題の一つである。なかでも、平衡から離れた系の統計物理学を構成することは現代物理学の挑戦的な重要課題である。本講演では、この問題にAdS/CFT対応を応用し、従来とは異なる視点から非平衡物理学を記述する試みについて解説する。AdS/CFT対応とは、ある種の量子ゲージ理論とある種の古典重力理論の間の対応関係である。この対応を用いると、非閉じ込め相にあるゲージ粒子の多体系はブラックホール時空にマップされる。通常、温度やエントロピーといった巨視的物理量は微視的自由度の粗視化で得られるが、ブラックホール時空の場合、微視的理論と巨視的物理量をつなぐのは重力の古典方程式であり、具体的な統計分布の知識は顕わに必要とされない。この性質は、統計分布が明らかでない非平衡系の記述には強力な武器となり得る。本講演では、この重力の不思議な性質を利用し、非平衡系の統計的性質を探ってゆく。いったん平衡系が重力理論で準備されれば、外力でドライブすることで非平衡統計系を準備できるが、AdS/CFT対応では、外力の線形応答を超えた領域の計算が、比較的平易な古典方程式を解くことで遂行可能となる。当日の講演は２部に分け、前半はAdS/CFT対応一般の導入的解説を、後半は講演者らが最近精力的に行っている、非平衡定常系の物理学へのAdS/CFT対応の応用に関して解説する予定である。

link: http://www.th.phys.titech.ac.jp/Nuclth/cafe/cafe.html

07/18

15:00

RIKEN main building, room 124-126

Toshiyuki Gogami(後神利志) (Kyoto University)

Spectroscopic research of \Lambda hypernuclei with high quality electron beam at Jefferson Lab

See here (PDF file).

04/18

13:00

RIKEN main building, room 124-126

佐藤大輔 (理研 河野低温物理研究室)

2次元ヘリウム3の基底状態

希ガス等の中性の原子間にはファンデルワールス的な引力相互作用が働くために、通常、十分低温まで冷却すれば原子気体は凝縮をおこし液体や固体を形成する。しかし、ヘリウム原子のような量子性の高い原子においては、これは必ずしも自明ではない。特に2次元面内に閉じ込めたヘリウム3は、凝縮による引力相互作用からの利得と零点エネルギー等による損失が拮抗していることが知られており、その基底状態が気体であるか液体であるかについては主に理論計算によっていくつもの研究が行われてきた。しかし、その多くは基底状態が気体であることを示唆するものであった。 最近、私は原子レベルで平坦なグラファイト基板上に単原子相ヘリウム3を吸着させ、フェルミ縮退温度域（2 < T < 80 mK）での熱容量測定によってその基底状態が気体であるか液体であるかを調べたところ、ヘリウム3が1 nm^-2以下の非常に希薄な密度の液体を形成していると考えられる結果を得た[1]。さらに、この液体は2次元面内への閉じ込めポテンシャルが大きく異なるグラファイト上1層目・2層目・3層目においても同程度の密度で現れており、このことから、ここで得られた結果は、厳密な2次元系においてもヘリウム3の基底状態が液体状態であることを示唆するものではないかと考えている。 [1] D. Sato, K. Naruse, T. Matsui, and H. Fukuyama, Phys. Rev. Lett.109, 235306 (2012); D. Sato et al., J. Low Temp. Phys. 158, 201 (2010).

12/17

15:00

RIKEN main building, room 213

Hyun-Chul Kim (Inha University)

Transverse charge and spin structures of the pion and the nucleon

The transverse charge and spin densties provide a novel aspect on the structure of the nucleon, since they reveal internal quark-gluon structures of the nucleon. We review a series of recent works on the transverse charge and spin densities of the pion and the nucleon, based on the chiral quark-(soliton) model. We first discuss the transverse spin densities of the pion, which can be obtained from the electromagnetic and tensor form factors. We then discuss the transverse charge and spin structures of the nucleon. In particular, we report the first results of the transverse strange charge and spin densities. Finally, we also show how the transverse charge densities undergo changes in nuclear matter based on the Skyrme model.

12/10

16:00

RIKEN main building, room 213

Yasuhiro Yamaguti (山口康宏) (大阪大学核物理研究センター)

Exotic baryons from a heavy meson and a nucleon

近年重いフレーバーの領域(チャーム・ボトム領域)では、KEK-BelleやSLAC-Babarを中心に「XYZ」と呼ばれる新粒子の発見が相次いでいる。 これらは単純なクォーク模型では説明することが難しいエキゾチックな構造を持っているが、なかでもメソン-反メソンの閾値近傍では、そのメソン-反メソンが緩く束縛した「ハドロン分子状態」とよばれる構造を持った粒子の存在が議論されている。 重いフレーバー領域でこのようなハドロン分子状態が形成される大きな要因として、この領域に現れるヘビークォークスピン対称性とそれにより強調されるパイオン交換力による重要な働きが考えられる。ヘビークォークスピン対称性はヘビークォークの質量m_Qが無限大の極限で現れる。このとき、クォーク間のスピン-スピン力は1/m_Qで抑制されてしまうため、ヘビー擬スカラーメソンとヘビーベクターメソンの質量の縮退が起こる。実際にストレンジネス領域のK*メソンとKメソンの質量差に比べて、ボトム領域のB*とB、チャーム領域のD*とDの質量差は非常に小さい。そのため、ヘビーフレーバー領域では、DD*pi vertexを通して働くパイオン交換力が強調される。 パイオン交換力の中でも特にテンソル力と呼ばれる力が強い引力を生み出す事はすでに原子核物理で知られており、ヘビーメソン系でも同様にハドロン分子状態を形成する原動力となることが期待される。 本研究では、パイオン交換力による強い引力に着目し、ヘビーメソンとバリオン(核子)による新たなハドロン分子状態の存在可能性について議論する。ヘビーメソンとして、反DメソンとBメソンを取り扱い、核子との間でクォーク-反クォーク対消滅が起こらない真にエキゾチックな状態(ペンタクォーク状態)を考える。2体系として反DN(BN)状態、そして3体系である反DNN(BNN)状態について束縛・共鳴状態の解析を行い、結果として閾値近傍に多くの状態が現れることを予言した。

12/03

15:00

RIKEN main building, room 213

Jiangming Yao (堯江明) (Tohoku University and Southwest University)

Beyond mean‐field description of impurity effect of Lambda hyperon on nuclear collective excitations

See here (PDF file).

11/08

15:00

RIKEN main building, room 213

Y. Taniguchi (University of Tsukuba)

Cluster correlations in deformed states

Structures of deformed states in sd-shell nuclei are discussed focusing on cluster correlations. Recently, rotational bands of largely deformed states have been observed by \gamma-spectroscopy experiments in A \sim 40 region such as 36,40Ar, 40Ca and 44Ti. Some of the deformed states are strongly populated by cluster-transfer reactions. In order to understand those properties, both of clustering and deformations should be taken into account. I will briefly introduce basics of clustering and deformations in nuclei, and discuss cluster correlations in largely deformed states of A \sim 30-40 nuclei such as Si, S, and Ca isotopes.

10/21-25

RIKEN main building

List of speakers is here

Workshop: "Multi-particle resonances and astrophysical reaction problems in few-body systems"

The details of this workshop: program and photo

08/28

13:30

RIKEN main building, room 213

Ellena Botta (INFN - Sezione di Torino and Torino University)

Highlights on n-rich $\Lambda$-Hypernuclei from the FINUDA experiment

See here (PDF file).

05/27

14:00

RIKEN main building, room 213

N. Yamanaka (Kyoto University)

Electric dipole moments and supersymmetric CP violation

The electric dipole moment (EDM) is an observable sensitive to the CP violation, with very small standard model prediction, and it is a very good probe of new physics beyond the standard model. In this talk, we will present the physics of the EDM from the elementary to nuclear level together with our works, by focusing on the supersymmetry as the leading candidate of new physics. We will also discuss the possibility to constrain the supersymmetric CP phases with prospective experiments.

03/18

14:00

RIKEN main building, room 213

T. Takahashi (Gunma National Cllege of Technology)

Charmed hadron coupling constants from Lattice QCD

We study charmed-hadron coupling constants based on 2+1-flavor lattice QCD. By computing hadronic form factors, coupling constants between charmed-hadrons and mesons (D*D\pi, DD\rho, DD*\rho) are evaluated. We discuss the flavor-SU(4) symmetry breaking in coupling constants, and evaluate electromagnetic radii of light and charm quarks in charmed mesons. (If possible) We will show our preliminary results of charmed-baryon couplings.

02/05

16:00

RIKEN main building, room 213

Yongseok Oh (Kyungpook National University)

Properties of hyperons with multi strangeness

The operation of J-PARC opens a new window for studying hyperons. In this talk, several interesting problems in hyperon spectrum which can be investigated at J-PARC will be discussed. We first discuss the strong model-dependence of Xi and Omega hyperon spectrum and the issue on the structure of several hyperon resonances. Then the question on the determination of spin-parity quantum numbers of Xi hyperons will be shortly mentioned.

12/10

16:00

RIKEN main building, room 213

S.X. Nakamura (YITP)

Dynamical coupled-channels model for meson productions and
application to strange nuclear physics

Modern experiments require sophisticated analysis tools for interpreting and extracting interesting physics from their data. For hadronic and/or nuclear reactions, such analysis tools are often theoretical models constructed with hadronic degrees of freedom. As such, I discuss a dynamical coupled-channels model developed for analyzing meson-baryon reaction data, thereby extracting baryon resonances. This dynamical model also has a great potential, with some extensions, for analyzing J-PARC data, and studying strange nuclear physics. I will discuss our ongoing effort towards this direction.

11/13

16:00

RIKEN main building, room 213

James S. M. Anderson (Univ. of Tokyo)

GKCI Approach for Solving the Electronic and Nuclear Schroedinger Equation

Achieving high accuracy in both electronic and nuclear structure computations is a priority when developing a structure method. The full configuration interaction (Full-CI) method achieves the highest accuracy within a model space, but is very computationally expensive (exponential scaling). Full-CI is a robust method that can be used with any Hamiltonian. It does not take advantage of the inherent smoothness associated with the solutions to the electronic and nuclear structure Hamiltonians. In the nuclear structure problem simplicity arises from every nucleon being identical (in the isospin formalism), and that the Hamiltonian only contains one- and two-body symmetric operators (though three-body operators are becoming more prominent). The same is true in the electronic structure problem. Our approach takes into account these symmetries that are neglected in the Full-CI approach. Results from Griebel[1] and others[2-4] in the mathematics of complexity literature show how one may construct a truncated Full-CI that has polynomial scaling but maintains Full-CI accuracy (at least within the large model space limit). We refer to this approach as GK-CI.[5] A special case of the method is similar to the no-core shell model. In this presentation the mechanics of the approach will be explained as well as preliminary results. References 1. M. Griebel and S. Knapek, Constr. Approx. 16, 525 (2000). 2. H. Bungartz and M. Griebel, Acta Numer. 13, 147 (2001). 3. G.W. Wasilkowski and H. Wozniakowski, Found. Comput. Math., 5, 240 (2005) 4. S.A. Smolyak, Dokl. Akad. Nauk 4, 240 (1963) 5. J.S.M. and P.W. Ayers, J. Chem. Phys., J. Chem. Phys. Submitted (2011).

11/12

14:30

RIKEN main building, room 213

D. Satow (Kyoto. U)

Ultrasoft Fermion Mode in Hot or Dense Boson-Fermion System

Investigation of fermion spectrum in a boson-fermion system such as QED/QCD at high temperature (T) or chemical potential (μ) is very important because it gives us the information on the basic building block of the system. In contrast to the case that the energy scale is of order gT or gμ (g: coupling constant), in which the method for perturbative analysis called "hard thermal/dense loop approximation" has been established, perturbative analysis in p<< g^2T region is difficult because of the infrared singularity. In this seminar, we find a novel fermionic excitation and obtain the expression of the dispersion relation, the decay width, and the strength, using the resummed perturbation theory regularizing that singularity in a hot QED/QCD plasma. We also find that the excitation disappears in the high density case, and discuss the reason of the disappearnce. Finally we derive the new generalized Boltzmann equation which is equivalent to the resummed perturbation from Kadanoff-Baym equation. By using that equivalence, we discuss kinetic interpretation of the resummed perturbation scheme, and show that the terms whose origin is different from those in the Boltzmann equation, appear in that kinetic equation.

10/29

16:00

RIKEN main building, room 213

Chiho Nonaka (Nagoya. U)

Dynamical model based on relativistic hydrodynamics for relativistic heavy ion collisions

Since the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) started its operation in 2000, a lot of discovery has been made and a lot of insight related to quantum chromodynamics (QCD) phase transition and the Quark-Gluon Plasma (QGP) has been gained. One of the most physically interesting and surprising outcomes at RHIC is the production of the strongly interacting QGP (sQGP). Besides, at Large Hadron Collider (LHC) heavy ion collision experiments started in 2010. To understand experimental data at RHIC and LHC comprehensively, construction of realistic dynamical model for description of relativistic hydrodynamic model is indispensable. First I outline the modeling of a realistic dynamical model based on relativistic hydrodynamics for comprehensive description of high energy heavy ion collisions. Comparing theoretical calculations and experimental data at RHIC and LHC, I will give brief explanation of the key ingredients for the construction of a multi-module model: initial condition, hydrodynamical expansion, hadronization, and freezeout processes. Then I will discuss our recent development of state-of- the-art relativistic viscous hydrodynamic model and its application to relativistic heavy ion collisions.

07/23

RIKEN main building 4F conference room 435,437

Dr. Nobutoshi Yasutake [安武 伸俊] (Chiba Inst. Tech.)

Thermodynamical description of hadron-quark phase transition and its
implications on compact-star phenomena

One of the most promising possibilities may be the appearance of quark matter in astrophysical phenomena in the light of recent progress in observations. The properties of deconfinement is not well understood, but the thermodynamical aspects of hadron-quark (HQ) phase transition have been extensively studied in recent years. Then the mixed phase of hadron and quark matter becomes important; the proper treatment is needed to describe the HQ phase transition and derive the equation of state (EOS) for hadron-quark matter, based on the Gibbs conditions for phase equilibrium. We here use a realistic EOS for hyperonic matter in the hadron phase. For quark matter we further try to improve the previous EOS by considering other effective models of QCD. One of the interesting consequences may be the appearance of the inhomogeneous structures called ”pasta”, which are brought about by the surface and the Coulomb interaction effects. We present here a comprehensive review of our recent works about the HQ phase transition in various astrophysical situations: cold catalyzed matter, hot matter and neutrino -trapped matter. We show how the pasta structure becomes unstable by the charge screening of the Coulomb interaction, thermal effect or the neutrino trapping effect. Such inhomogeneous structure may affect astrophysical phenomena through its elasticity or thermal properties. Here we also discuss some implications on supernova explosion, gravitational wave and cooling of compact stars.

07/09

16:00

RIKEN main building, room 213

Mr. Zhou Bo [周 波] (RCNP)

New concept for the ground-state band in 20Ne within a microscopic
cluster model

About a decade ago, the THSR (Tohsaki, Horiuchi, Schuck, Ropke) wave function was proposed, which has been quite successful in describing the dilute gas-like states in light nuclei and indeed leads us to have a new perspective for the n alpha cluster structure in light 4n nuclei. Now, we propose a generalized wave function based on the flexible original THSR wave function , which is applicable to studies of general cluster structures in nuclei. The ground-state band in 20Ne is investigated by using this generalized wave function and the energies obtained agree well with the experimental values. Moreover, it is found that the single generalized THSR wave functions almost completely coincide with the exact solutions of alpha+16O resonating group method for the ground-state band in 20Ne. For the ground state, for instance, the squared overlap between them is 99.3%. Therefore we have a new concept for understanding the compact structure of the ground-state band in 20Ne, which provides a more exact picture than the Brink cluster model. On the other hand, we can conclude that the THSR model wave function can also be extended to study more compact cluster states in nuclei such as, e.g., the ground-state band in 20Ne.

06/29

16:00

RIKEN main building, room 213

浦田 靖子 (東北大学)

Coulomb Breakup and Reaction Cross Sections for Deformed Halo Nucleus ^{31}Ne

A halo structure with an extended density distribution is one of the characteristic features of weakly bound neutron-rich nuclei. For the neutron-rich nucleus^{31}Ne, the halo structure has been recently suggested by the experimental data of Coulomb breakup and interaction cross sections measured at RIKEN RIBF facility. Assuming that^{31}Ne consists of the strongly deformed core nucleus^{30}Ne and one valence neutron, we calculate Coulomb breakup and reaction cross sections of^{31}Ne taking into account the rotational excitation energy of the core nucleus^{30}Ne with particle-rotor model (PRM). We will discuss the structure of^{31}Ne deduced from these calculations.

05/28

16:00

RIKEN main building, room 213

井坂 政裕 (北海道大学)

Structure study of p-sd shell and neutron-rich $\Lambda$ hypernuclei by
using AMD

In this talk, we will discuss the structure of several p-sd shell and neutron-rich $\Lambda$ hypernuclei such as Be, Ne and Mg, based on the antisymmetrized molecular dynamics (AMD) calculation. Forthcoming experiments at J-PARC will reveal the spectroscopy of sd-shell and neutron-rich $\Lambda$ hypernuclei. One of the unique and interesting aspects of hypernuclei is the structure change caused by hyperon. Through the interaction with surrounding nucleons, a hyperon in the atomic nucleus can affect and modify nuclear clustering and deformation. Especially, the structure changes of sd-shell and neutron-rich $\Lambda$ hypernuclei are of interest, since the various clustering and deformed structures coexist in the ground and low-lying excited states. To study such phenomena, we have extended the AMD for hypernuclei and applied it. By using the YNG and Gogny D1S as effective $\Lambda$N and NN interactions, we investigated the low-lying structure of Be, Ne and Mg $\Lambda$ hypernuclei without any assumption on the clustering and deformation. In this talk, we will show you the excitation spectra of such $\Lambda$ hypernuclei and discuss the structure changes caused by $\Lambda$ hyperon.

05/23

16:00

RIBF Building, 2F large meeting room

【肥山研・中務研共催セミナー】 民井 淳(RCNP)

Tensor Correlation in the Ground States of N=Z Nuclei

The nucleon-nucleon (NN) interaction contains a strong tensor interaction due to pion exchange. The strong attraction of the tensor interaction contributes significantly to the binding energy of nuclei. Therefore it is natural to treat the tensor interaction explicitly in nuclear structure calculations. Such calculations are, however, limited in few-nucleon systems due to mainly technical difficulty. Thus the role of the tensor interaction, or tensor correlation, in nuclear structure has not been explicitly taken into account in conventional shell-model and mean-field calculations, and has been hidden. Experimental trial for probing the effects of tensor correlation is one of hot topics. We have recently observed bulk contribution of the tensor correlation in the ground states of self-conjugate (N=Z) even-even nuclei. The experiment was performed at the Research Center for Nuclear Physics (RCNP), employing a high-resolution proton beam at 295 MeV and the Grand Raiden spectromter. Spin-M1 transition strengths from the ground states of^{12}C,^{16}O,^{20}Ne,^{24}Mg,^{28}Si,^{32}S,^{36}Ar, and^{40}Ca nuclei have been determined for each of isoscalar and isovector transitions up to 16 MeV. The observed transition strengths are converted, by using a sum-rule, to an expected value of the ground state wave-function ＜S_p . S_n＞, where S_p(n) is the vector-sum of all the proton (neutron) spin-operators. The value is quite sensitive to the tensor correlation between protons and neutrons. The extracted number is ~0.1 and is more or less flat in sd-shell region. The number is consistent with predictions for the 4He nucleus using realistic NN interactions. I will report on the experiment and discuss the results.

05/14

14:30

RIKEN main building, room 213

滑川 裕介 (筑波大)

Charm quark physics from lattice QCD

We investigate the charm quark system using the relativistic heavy quark action on 2+1 flavor PACS-CS configurations. The dynamical up-down and strange quark masses are set to the physical values by using the technique of reweighting to shift the quark hopping parameters from the values employed in the configuration generation. The charm quark mass is determined by the spin-averaged mass of the 1S charmonium state. We also calculated the Cabibbo-Kobayashi-Maskawa matrix elements, |V_{cd}| and |V_{cs}|, extracted from the charmed and charmed-strange meson decay constants.

05/07

16:00

RIKEN main building, room 213

森田 健司 (京大基研)

Baryon number probability distribution in the presence of second order phase transition

We discuss the probability distribution of a net conserved charge based on the Landau theory of phase transition. Statistical fluctuations of the net baryon number, especially of higher orders, have been regarded as diagnostics of the chiral phase transition in QCD. Normally they are discussed by calculating cumulants of the net baryon number through derivatives of the thermodynamic pressure with respect to the chemical potential in the grand canonical ensemble. Lattice QCD and effective model calculations have revealed their critical behaviors in the vicinity of the chiral phase transition. The purpose of this work is to characterize the critical behavior in terms of the probability distribution. We construct an analytically solvable model which respects relevant symmetries based on the Landau theory within mean field approximation. We clarify differences in the probability distribution originated from the singular part of the thermodynamic potential. Then, we consider an extension by implementing O(4) critical scaling in the model pressure such that higher order cumulants (c3 and c4) diverge at the phase transition. We emphasize the relationship of the probability distribution to the analytic structure of the grand canonical partition function in complex chemical potential. It is pointed out that the singular structure, which gives the divergent cumulants, leads to an anomalous oscillatory factor in the probability distribution through both numerical calculations and analytic consideration.

04/23

16:00

RIKEN main building, room 213

Lie Ang

Massive neutron stars and the equation of state of matter at high densities

We perform Brueckner-Hartree-Fock calculations of kaon-condensed matter, hypernuclear matter and hybird matter, and compute the structure of neutron stars within this approach. We conclude that kaon condensation may be totally suppressed in our model, but low maximum masses below 2 solar masses are found for hyperon stars and hybrid stars.

04/17

11:30

RIKEN main building, room 213

作道直幸 (東京大学 理学系研究科 物理学専攻 上田正仁研究室)

Lee-Yangの量子クラスター展開法を用いた非対角長距離秩序の判定条件

ユニタリー・フェルミ気体の熱力学関数が、３つのグループにより実験的に計測された[1]。これらの実験結果を解析する理論的なアプローチの一つとして、フガシティz=exp(βμ)による展開（クラスター展開）が注目されている。多くの先行研究により、3次や4次の低次の係数が数値的に求められた[2]。しかし、相転移を扱うには、高次の項を取り入れる必要がある。我々は、クラスター展開の高次の項を系統的に扱うために、Lee-Yangの量子クラスター展開法[3]を拡張した[4]。拡張された方法を用いれば、ボース系やフェルミ系の大分配関数とN 粒子還元密度行列が、ボルツマン統計で定義された同じ系のクラスター関数を用いて、系統的に計算できる。この方法は、展開を数学的に正当化でき、一様系でもトラップ系でも使える。今回の拡張により、ボース系やフェルミ系の「非対角長距離秩序（ODLRO）の発現」の有無を調べることができる。得られたODLROの判定条件は、収束する無限和で表される。セミナーでは、関連する最近の研究[5, 6]についても簡単に触れる予定である。 [1] M. Horikoshi et al., Science 327, 442 (2010); S. Nascimbne et al., Nature 463, 1057 (2010); M. J. H. Ku et al., Science, 335, 563 (2012). [2] G. Rupak, PRL 98, 090403 (2007); X.-J. Liu et al., PRL 102, 160401 (2009); D. B. Kaplan and S. Sun, PRL 107, 030601 (2011). [3] T. D. Lee and C. N. Yang, Phys. Rev. 113, 1165 (1958); 117, 22 (1960). [4] N. Sakumichi, N. Kawakami and M. Ueda, Phys. Rev. A 85, 043601 (2012). [5] N. Sakumichi, N. Kawakami and M. Ueda, arXiv:1202.6532 (2012). [6] N. Sakumichi, Y. Nishida and M. Ueda, in preparation.

04/16

14:00

RIKEN main building, room 213

Koike Takahisa

Formation of light Xi^- hypernuclei via (K^-, K^+) reaction

The Xi-N interaction is not well-known, other than it could be weakly attractive. An experimental search of Xi^- hypernucleus via (K^-, K^+) reaction on 12C target is planned at J-PARC as E05. Many authors have theoretically performed the calculation of (K^-, K^+) reaction spectra on 12C and the heavier targets with the closed shell, while none for the lighter target than 12C so far. On the other hand, Hiyama et al. have predicted the existence of Xi^- hypernuclear bound state for several light $p$-shell nuclei by the few-body structure calculation. Thus, our purpose is to calculate the (K^-, K^+) reaction spectra on light p-shell targets and examine their experimental feasibility. In this talk, we focus on the 7Li target case, which forms [Xi^- + 6He] bound state via (K^-, K^+) reaction. The expected reaction spectrum is calculated within the framework of distorted wave impulse approximation (DWIA) using coupled-channel Green's function method considering [Xi^- + 6He(0+)]-[Xi^- + 6He(2+)] channel coupling.

04/09

13:00

RIKEN main building, room 213

Suno Hiroya [PPT]

A diabatic hyperspherical study of traiatomic helium systems

Luncheon Seminar

03/05

15:00-

RIKEN main building, room 213

Shigehiro Nagataki (YITP)

General Relativistic Magneto-Hydrodynamic Simulations of Gamma-Ray Bursts

Gamma-Ray Bursts (GRBs) are the most powerful explosions in the Universe. Recently, it is found that some GRBs are born with peculiar supernova explosions. The explosion energy of the peculiar supernovae is about 10 times greater than that of normal supernovae. That is why it is believed that the central engine of GRBs is different from the one of normal supernovae. However, it is not known well how the engine of GRBs is working. In this talk, I would like to review the history of the study on the central engine of GRBs and I would like to present my recent numerical simulations (General Relativistic Magneto-Hydrodynamic Simulations) of the engine. Also, I would like to show briefly some our recent works that are related with GRB phenomena.

12/22

15:00-

RIKEN main building, room 213

Hideko Nagahiro (Nara Women's University) [PPT]

Composite and elementary natures of hadrons

-- Study of mixing properties of a1(1260) --

-- Study of mixing properties of a1(1260) --

One of recent interests in the hadron structure is whether hadrons are made up of quarks and gluons confined in a single-particle potential as described in the conventional quark model, or rather develop subcomponents of quark-clusters inside hadrons. It has been suggested that some hadronic resonances could have substantially large components of hadronic composites. In view of the fact that hadronic resonant states are unavoidably mixture of hadronic and quark-composites, an important issue is to clarify how these components are mixed in a hadron. In this talk, we focus on hadron structure having two components of hadronic composite and elementary component, by taking the a1(1260) meson as an example. The problem is analyzed in a manner similar to a two-level problem with mixing in quantum mechanics. We propose a method to disentangle their mixture appearing in the physically observed state.