Elucidation of New Hadrons with a Variety of Flavors


Quarks, the elementary building blocks of material, act under Quantum Chromo Dynamics (QCD). The universe is so cool today that a quark can not exist alone, thus quarks as well as antiquarks form hadrons and nucleus. Various dynamics, such as color confinement, dynamical mass generation and spontaneous chiral symmetry breaking, affect the process of hadron formation. However, the detailed mechanism of those dynamics is still unknown. In addition, though success of constituent quark model enable us to categorize the hadrons found by the accelerator experiments carried out during 20th century into mesons consisting of quark-antiquark and baryons being made up of tri-quarks, we do not have the QCD-based understanding of the reason why other configurations are so suppressed. Here, the unresolved questions are; how the constituent quarks get masses? and what kinds of hadrons can be formed?

During the first decade of this century, several epoch-making experimental results have been brought by Japanese projects/research activities. In 2003, LEPS experiment at SPring-8 reported evidence of the exotic baryon named Theta+ containing 5 quarks involving a s-quark. From Belle experiment at KEK B-factory discovered many charmonium-like exotic hadrons, namely, X(3872), Z(4430)+ and so on. E325 experiment at KEK-PS (phi experiment) made the first observation of the fact that masses of vector mesons (rho, omega and phi) decrease in nucleus. Japanese researchers' contributions are also remarkable in theoretical work, hadron spectroscopy and interaction in quark model, dynamics based on chiral symmetry and numerical approach by lattice QCD. Thus, Japan has the world-class activities in hadron physics.

This research project aims to gather worldwide leading experimentalists and theorists, who have been carrying out their research with each accelerator facility in relatively independent manner, to establish new hadron physics field at crossover region between particle and nuclear physics. For exotic hadrons, B-factory electron-positron collider experiment (Division A01) is a suitable place to research charmed/bottomed exotic mesons and SPring-8/J-PARC facilities (Division B01) bring us opportunities to investigate exotic strangeness baryons produced by proper fixed target experimental setups. The interplay of these activities is quite important to make exotic hadrons' properties clear by a variety of flavors. Together with these, the core of experimental research of this project has the attempt to reveal hadron's mass generation mechanism (Division C01). Since all the experiments mentioned above aim luminosity/intensity upgrade plans, the detector technology development performed in coherent way (Division D01) is desired to make progress efficiently. The key role of theoretical studies (Division E01) is finding the way to elucidate the mechanism of quark confinement, hadrons' mass generation and chiral symmetry breaking by carefully looking into experimental results in a consistent viewpoint. The project organization mentioned above is in order to bring many fruitful results by on-going or nearly starting experiments. Such achievement must make sure the evolution to future higher level experiments.

As the result of this project, if pentaquark and tetraquark states are established, those are totally new style of quark matter beyond conventional mesons and baryons of quark model. Such fact would become a striking trigger to make Super B-factory, LEPS2 and J-PARC experiments evolve much, and then progress of our understanding about quark confinement and mass generation mechanism would be dramatic. Thus there will be new physics field at crossover region between particle and nuclear physics.

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