Mesonbaryon

Meson-baryon refers to a system consisting of a meson, a bosonic hadron made of a quark-antiquark pair, and a baryon, a fermionic hadron composed of three quarks. In quantum chromodynamics, these systems interact via the strong force and are studied to understand non-perturbative hadron dynamics. Meson-baryon interactions can form resonances or quasi-bound states and contribute to the observed hadron spectrum beyond simple three-quark baryons or quark-antiquark mesons.

Common processes include pion-nucleon scattering (πN), kaon-nucleon (K̄N) scattering, and various coupled channels where several meson-baryon configurations mix with each other through strong interactions. The quantum numbers that classify these states include total angular momentum and parity J^P, isospin I, and strangeness S, among others.

Many resonances in the strangeness -1 and -2 sectors are interpreted as dynamically generated meson-baryon states in modern approaches. A prominent example is the Lambda(1405), frequently described as arising mainly from K̄N and πΣ coupled channels rather than a single three-quark state. Similar ideas apply to other Λ*, Σ*, and N* states discovered in scattering and photoproduction experiments.

The theoretical description often uses chiral effective field theories with coupled-channel unitarization, or lattice QCD studies of hadron-hadron interactions. These frameworks aim to explain the spectrum and reactions while connecting to underlying QCD.

Meson-baryon dynamics illuminate how quark and meson degrees of freedom reorganize at low energies and contribute to the broader understanding of non-perturbative QCD and hadron structure.