Elucidation of New Hadrons with a Variety of Flavors

Theoretical Study

Research Project E01: Theoretical Study on new aspects of quark-hadron matter with various flavors

Quantum Chromodynamics and hadron physics

Strongly interacting hadrons (nucleons and mesons) are governed by Quantum Chromodynamics (QCD) of the standard model. However, quarks and gluons are, though fundamental particles, confined in hadrons and the mechanisms of how hadrons are formed by them are not yet understood (problem of hadron formation). In the formation of hadrons, mass is also expected to be generated through the spontaneous breaking of chiral symmetry. A very fundamental question on the origin of the matter has not yet been understood.

New types of hadrons

Signals of new types of hadrons have been observed in 2002 and 2003. They were the Θ particle at SPring-8/LEPS, which is a candidate for pentaquark, and X(3872) at KEK/Belle, which is a candidate for tetraquark. Triggered by these observations recent research activities have focused on the new particles, known as “exotic hadrons”. Since these observations, new particles have been found at Belle, called X, Y, and Z. By exploring the properties of these exotic particles we are aiming to understand the formation mechanisms of hadrons from quarks.

Mass generation

The origin of mass is a fundamental question. Physicists now believe that mass is generated by interactions, causing the spontaneous breaking of chiral symmetry. However, this idea, proposed by Prof. Nambu, has not yet been confirmed in experiments, nor has it been derived from QCD. In 2007, a hadron experiment at KEK suggested that the mass of φ meson was decreased in nuclear matter. This indicates that mass is dynamically generated by QCD interactions and is the first evidence of the Nambu’s idea of dynamical mass generation.

Research purpose

We are expecting to obtain a vast amount of data from hadron experiments which will be conducted at LEPS2, J-PARC, and KEK-B. Based on these data and the fundamental principle of QCD, we perform theoretical studies to clarify new hadronic states and the dynamical mechanisms of mass generation in order to investigate the fundamental questions of the formation of matter. In particular, we are conducting theoretical research by collaborating with elementary particle and nuclear physicists. As theoretical studies, we not only explain experimentally-observed phenomena but also predict new phenomena and methods. We also emphasize intimate communications with experimental groups.

Methods of research

Quark models, Effective chiral models, Lattice QCD, Gauge/gravity theory, Perturbative QCD, Reaction study and any other methods for exploring hadron physics. In particular, we welcome new ideas.

Research activities

Actively hiring young researchers
Conducting international collaborations
Organizing international research meetings and schools for encouraging young researchers

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