Lighthadron

Lighthadron is not a standard term in contemporary particle physics. When encountered, it typically refers to hadrons composed of light quarks (up and down) and, in some contexts, the strange quark. This usage overlaps with the conventional category of light hadrons, by contrast with heavy hadrons that contain charm, bottom, or top quarks. Light hadrons include mesons, which are quark–antiquark bound states, and baryons, made of three quarks.

Representative light hadrons include pions (π), kaons (K), nucleons (protons and neutrons), and light hyperons. Pions and kaons are among the lightest mesons; nucleons are the lightest baryons. Light hadrons appear in various spin states: pseudoscalar mesons (spin 0), vector mesons (spin 1), and baryons with spin 1/2 or higher.

Their dynamics are governed by quantum chromodynamics (QCD). At low energies, they are described by effective theories such as chiral perturbation theory, while lattice QCD provides first-principles calculations of their masses and interactions. Their properties reflect spontaneous chiral symmetry breaking, with pions acting as pseudo-Goldstone bosons that dominate many low-energy processes.

Light hadrons are produced in high-energy collisions and in cosmic-ray interactions. Many decay via the weak interaction, with lifetimes typically on the order of 10^-8 to 10^-10 seconds for mesons, while nucleons are effectively stable on detector timescales. Observables include masses, lifetimes, decay modes, and scattering properties, which test QCD and the symmetries of the Standard Model.

Note: the term "lighthadron" is not widely used in formal literature; "light hadron" or "light-quark hadron" is the preferred terminology.