Research Groups

A01 Dynamics to bridge quark and hadron hierarchies

Kenta Shigaki (Hiroshima University)

 We aim at elucidating the behavior of deconfined quarks and the dynamics of hadron formation at the ALICE experiment at CERN in Switzerland. Quarks are freed from confinement inside hadrons and turn into the Quark Gluon Plasma phase in high energy nucleus-nucleus collisions. Chiral symmetry restoration phenomena are expected with modified strongly coupled quark pair condensate in the transitions to the high temperature quark phase and back to hadrons. Semi-clusters bridging the quark and hadron hierarchies are looked for, utilizing rare phenomena characteristic and unique to this type of experiments, such as flavor dependent inter-quark interaction up to beauty quarks and production of exotic hadrons via recombination of quarks. The physics goals are only to be reached by measurements in the next stages with unprecedented precision and statistics covering wide kinematic regions. The ALICE detector is hence upgraded with an improved main tracking detector, a new forward tracker, and higher speed data taking, toward its third physics operation from 2021. The A01 plays the key role to unravel the most basic hierarchies of the many in the nature, which this entire Kakenhi project attacks.

A02 Elucidation of hierarchical structure between quark and hadron phases by means of quark clusters

Hiroaki Ohnishi (Tohoku University)

Hadrons, such as protons and neutrons, are known to be composed of elementary particles, i.e. quarks, bound together by the strong interaction. About 140 baryons (bound state of three quarks) and 180 mesons (quark-antiquark bound state) are experimentally established to date. Recently, many new types of hadrons which cannot be described in the framework of ordinary mesons and baryons structures, were discovered, such as tetra-quark mesons, penta-quark baryons and meson-baryon molecule states, etc., especially in the energy region overlapping with excited states of mesons and baryons. Those type of states are called exotic hadrons. Discoveries of exotic hadrons are opening new questions in the hadron picture, i.e. what is the mechanism and/or conditions of the transition between ordinary meson/baryon to exotic hadrons?

To answer these questions, the A02 project will perform two experiments focusing on baryon spectroscopy, one at J-PARC with high energy hadron beam and a second one at SPring-8/LEPS2 with high brightness gamma ray. Detail description for each one of these measurements is as follows.

1) J-PARC: A large solid angle charged particles spectrometer (Heavy Baryon Spectrometer, HBS) will be constructed on high momentum beam line (high-p) at J-PARC. Through the spectroscopy of charmed baryons (Λc*) and strangeness(S) = -1 and -2 baryons (Λ*,Ξ*) by using HBS, we will obtain insight of the existence for clusters in baryons, i.e. di-quark correlations.

2) SPring-8/LEPS2: The LEPS2-Solenoid spectrometer will be constructed at SPring-8/LEPS2 beam line. By using LEPS2-Solenoid spectrometer and upgrading the intensity of gamma ray beam, the measurement of production cross sections and the decays for exotic hadron candidates (such as Λ(1405) and penta-quark baryons) will be performed, to reveal their structure, i.e. whether these states are hadron molecule states or not.

B01 Clusters of strange hadrons for investigating hierarchical structure of matter

Hirokazu Tamura (Tohoku University)


B02 Exotic nuclei for investigating hierarchical structure of matter

Takashi Nakamura (Tokyo Institute of Technology)

We aim to investigate 1) multi-neutron systems in neutron-rich exotic nuclei, and 2) three-nucleon forces (3N force). The former is relevant to dineutron clusters which may form a semi-hierarchy between nucleon(hadron)- and nuclear hierarchies, while the latter provides a key to understand the characteristic nuclear force (3N force) from the more fundamental level, such as from quark degree of freedom. The research projects we are planning are as follows:

1) Multi-neutron systems: Using the intense RI beams available at RIBF, RIKEN, extremely neutron-rich helium and oxygen isotopes beyond the neutron drip line are produced by quasi-free (p,pp) scatterings in inverse kinematics. We then investigate the expected 4n or 6n states revealed on the surface of extremely neutron-rich systems, such as 10He and 28O. We also investigate if these multi-neutron systems are composed of dineutrons. We clarify how such states are related to the threshold rule (as in the Ikeda Diagram for α clusters). We also investigate the spectroscopic factor (or purity) of the dineutron-cluster configurations.

2) 3N force: To clarify the transition from the quark hierarchy to the hadron and nuclear hierarchies, the three-nucleon forces with unexplored degree of freedoms are investigated. In particular, we perform the following two subjects: i) We develop new experimental probes for the 3N forces with the isospin triplet (T=3/2), namely the three-proton or three-neutron systems. ii) We realize the measurements of full spin observables in (p,pN) reactions, which can show significant 3N force effects as proposed in the recent theories.

C01 Ultracold atom study of exotic phenomena bridging different hierarchies

Yoshiro Takahashi (Kyoto University)

Recently an extremely high level of controllability of cold atomic system has been achieved. New possibilities are now explored by exploiting a magnetic Feshbach resonance method which enables us to dynamically control inter-atomic interactions in a precise way. In this research, we aim at the deeper understanding of the hierarchical structure of quantum matters by experimentally generating and studying an ultracold atomic mixture with an extremely large mass ratio. In particular, by developing a magnetic Feshbach resonance method for controlling the interaction between heavy and light atoms, we plan to observe a Efimov trimer as a universal cluster state, enabling the quantitative understanding of the separability, resolve the energy structure as a threshold law, observe the effective force between the heavy atoms through their interaction with the light atoms and the resulting superfluid phase transition of Fermi pairs, and study the universal phenomenon in a non-equilibrium dynamics known as Anderson orthogonality catastrophe. From these studies, we reveal the common physical phenomena bridging different hierarchies and few particles correlations as well as quantitative analysis of the separability, and deepen the understanding about the concepts characterizing the hierarchal structures such as phase transition, cluster, and force.

C02 Universal physics of quantum matter at the change of the hierarchy and the state

Munekazu Horikoshi (Osaka City University)

 The objectives of the C02 group are "understanding of the fundamental physics about fermion-pair formation as quantum cluster formation, bosonization of fermions as neutralization process of the degree of freedom, and the quantum many-body effects resulting from them” by using ultracold atomic gases as a “quantum simulator”. By using the quantum simulator, we experimentally measure the various thermodynamic quantities, the magnetic susceptibilities, and the transport coefficients as functions of scattering length, effective range, spin polarizability, and temperature in the wide parameter spaces. Then, we will show “the universal physical law of quantum cluster phenomenon” by comparing the experimental data with the condensed matter theory and the nuclear theory. Finally, we aim to contribute to elucidation of cluster phenomena in other particle hierarchy covered by this project.

D01 Emergence mechanism of hierarchical structure of matter studied by ab-initio calculations

Emiko Hiyama (Kyusyu University)

D02 member perform ab-initio calculation for hadron, nuclei, atom, molecular-systems, and investigate a mechanism to form hierarchical structure. At the same time, we encourage to develop each physics such as hadron, nuclear and atom-molecular physics, by exchanging discussion among these fields. The details are as follows:

(1) In hadron physics, we get useful information on hadron-hadron interactions by Lattice QCD calculation.

(2) With use of these interactions, we perform up to six-body calculations of hadron and nuclear systems and explore the mechanism of cluster formation of these systems.

(3) In addition, it is planned to study strong correlations between fermions. In the same manner, we perform ab-initio calculation for atomic and molecular systems taking into account of a degree of nuclei and clarify the difference and similarity in between atomic-molecular physics and hadron-nuclear physics. At the same time, we clarify the separability of hierarchical structure.

The above research should be fed back to the experimental projects such as A01, A02, B01, B02, C01, and C02 and can be contributed to the development of these experiment projects.