hadronized

Hadronized refers to the process by which quarks and gluons produced in high-energy interactions form hadrons, such as mesons and baryons. Because color confinement prevents free quarks and gluons, the perturbative evolution of partons ends in a nonperturbative regime where they combine into color-singlet states. Hadronization is a universal aspect of quantum chromodynamics (QCD) and is essential for connecting parton-level calculations to observable particles.

There are two broad classes of models used to describe hadronization in phenomenology. In string fragmentation models, exemplified by the Lund string model, the color field between separating partons forms a string that breaks by producing quark–antiquark pairs, yielding mesons and sometimes diquark pairs that produce baryons. In cluster (or color-singlet) models, color-neutral clusters decay into hadrons. Both approaches aim to reproduce observed hadron spectra, multiplicities, and particle ratios and rely on parameters tuned to data.

Hadronization is nonperturbative and cannot be calculated from first principles with current theory; instead, it is implemented in Monte Carlo event generators such as Pythia (string fragmentation), Herwig (cluster model), and Sherpa. Fragmentation functions describe the probability distribution for a parton to produce a given hadron with a particular momentum fraction; these functions are extracted from experimental data and used in global analyses.

Experimental signatures of hadronization include jet formation in e+e− and hadron colliders, with measured hadron spectra, ratios of mesons to baryons, and transverse momentum distributions. In heavy-ion collisions, hadronization may be modified by the surrounding medium as part of the transition from quark–gluon plasma to hadronic matter. Ongoing research seeks to improve the understanding of hadronization by integrating experimental results with nonperturbative QCD insights.