hadronization

Hadronization (or hadronisation) is the process of the formation of hadrons out of quarks and gluons. There are two main branches of hadronization: quark-gluon plasma (QGP) transformation and colour string decay into hadrons. The transformation of quark-gluon plasma into hadrons is studied in lattice QCD numerical simulations, which are explored in relativistic heavy-ion experiments. Quark-gluon plasma hadronization occurred shortly after the Big Bang when the quark–gluon plasma cooled down to the Hagedorn temperature (about 150 MeV) when free quarks and gluons cannot exist. In string breaking, new hadrons are forming out of quarks, antiquarks and sometimes gluons, spontaneously created from the vacuum.

== Statistical hadronization == A highly successful description of QGP hadronization is based on statistical phase space weighting according to the Fermi–Pomeranchuk model of particle production. This approach was developed, since 1950, initially as a qualitative description of strongly interacting particle production. It was originally not meant to be an accurate description, but a phase space estimate of upper limit to particle yield. In the following years numerous hadronic resonances were discovered. Rolf Hagedorn postulated the statistical bootstrap model (SBM) allowing to describe hadronic interactions in terms of statistical resonance weights and the resonance mass spectrum. This turned the qualitative Fermi–Pomeranchuk model into a precise statistical hadronization model for particle production. However, this property of hadronic interactions poses a challenge for the statistical hadronization model as the yield of particles is sensitive to the unidentified high mass hadron resonance states. The statistical hadronization model was first applied to relativistic heavy-ion collisions in 1991, which led to the recognition of the first strange anti-baryon signature of quark-gluon plasma discovered at CERN.