hadronize

Hadronize is the process by which quarks and gluons produced in high-energy interactions transform into hadrons, such as mesons and baryons. In quantum chromodynamics, color confinement prevents isolated color charges, so partons must combine into color-neutral states as they separate and the strong interaction becomes non-perturbative at low energy scales.

Hadronization occurs after hard scattering processes in contexts such as electron-positron annihilation, deep inelastic scattering, and hadron-hadron collisions. Energetic partons radiate gluons and branch into more partons (a parton shower), then non-perturbative dynamics reorganize them into hadrons, while conserving energy, momentum, and quantum numbers like baryon number and flavor.

Two widely used modeling approaches describe hadronization. Fragmentation, notably implemented in the Lund string model, envisions color strings breaking into quark-antiquark pairs to form hadrons. The cluster model groups color-connected partons into colorless clusters that decay into hadrons. In heavy-ion collisions, recombination or coalescence of nearby quarks can also contribute to hadron formation, particularly at lower momenta.

Experimental and computational tools reflect these ideas. Fragmentation functions quantify the probability of producing a hadron with a given momentum fraction from a parton. Event generators such as PYTHIA (string fragmentation) and HERWIG (cluster model) implement hadronization to produce realistic final states. Hadronization is inherently non-perturbative and introduces uncertainties in jet structure and precision measurements, while essential for connecting partonic processes to observed hadronic spectra.