hadrons

Hadrons are subatomic particles composed of quarks held together by the strong interaction, mediated by gluons. They are color-neutral objects due to color confinement and cannot exist as free quarks. Hadrons are traditionally divided into baryons, which contain three quarks, and mesons, which consist of a quark and an antiquark. In addition, more exotic forms such as tetraquarks, pentaquarks, glueballs (bound states of gluons), and hybrids (quarks with excited gluon fields) are studied in quantum chromodynamics.

In the quark model, baryons are made of three quarks (qqq) and mesons of a quark–antiquark pair (qq̄). Examples include the proton (uud) and neutron (udd) as baryons; pions (π+, π0, π−) and kaons (K+, K0) as mesons. Hadrons containing heavier quarks—charm (c) and bottom (b)—also appear, producing states such as heavy-flavor baryons and mesons like the J/ψ (cc̄) or Υ (bb̄). Hyperons, such as the Λ, Σ, Ξ, and Ω families, include strange quarks in their composition.

Hadrons have varying lifetimes and decay modes. Stable baryons like the proton are effectively permanent, while many hadrons decay through strong or electromagnetic processes, and some via weak interactions. The masses and spectra of hadrons reflect quark content, binding energy, and quantum chromodynamics dynamics, including contributions from sea quarks and gluons.

Hadrons are produced abundantly in high-energy processes and during hadronization in particle collisions. They serve as the primary carriers of strong-interaction dynamics in experiments and are central to studies of quantum chromodynamics and the structure of matter.