stringmelting

String melting is a mechanism used in the modeling of ultra-relativistic heavy-ion collisions, where color strings created in the early stage of the collision dissolve into deconfined quarks and antiquarks when the local energy density is high enough. This concept is most closely associated with the string-melting version of the AMPT (A Multi-Phase Transport) model, though related ideas appear in other hadronization schemes.

In string-melting models, the strings are replaced by a partonic medium: the color flux tubes melt into partons, which then undergo scatterings (a parton cascade) before hadronizing via quark coalescence, rather than fragmenting into hadrons. Hadronization proceeds through recombination of nearby quarks, which can enhance baryon production relative to mesons in the intermediate transverse momentum range. The approach aims to reproduce collective flow patterns observed in experiments, notably the approximately constituent-quark-number scaling of elliptic flow.

Critics note that string melting is a phenomenological construct with adjustable parameters, and its success depends on the collision system and energy. It remains one of several competing approaches to hadronization in dense QCD matter, alongside string fragmentation and other coalescence models. The term is typically written as "string melting" in literature, though some implementations refer to it as the string-melting version of a specific transport model.