What are essential degrees of freedom in hadrons? This is a fundamental question in hadron physics. Quarks are thought to be the most fundamental building blocks to form hadrons. Although the principal equation to describe the dynamics of quarks is known as the Quantum Chronodynamics (QCD),
the QCD is hardly solved in low energy due to its non-perturbative nature.
As a result, quarks are confined in hadrons.
The constituent quark model (CQM) well describes the properties of hadrons, such as masses, classification based on spin/flavor symmetry, magnetic moments of groundstate baryons, and so on so forth. In the CQM, constituent quarks act like Dirac particles, But sometimes fails in excited states. There remain many undiscovered states predicted by the CQM, which is a long-standing puzzle, known as the so-called missing resonance problem. The mass order of the resonance baryons Exotic states
In order to answer the above-mentioned questions in hadron physics, we need to understand the interaction between quarks in hadrons further. In particular, quark-quark correlation, namely diquark correlation, in a baryon is of interest. In light baryons, where flavor SU(3) symmetry seems to work rather well, 3 quark-quark pairs are expected to be correlated each other on equal foot. Extraction of a diquark correlation may not be easy.
Baryons with a heavy quark provide unique opportunities to study diquark correlation. Magnitude of the color-spin interaction between quarks is proportional to the inverse of the quark mass. One expects that the