Hadronization in small and large systems

Abstract

Recent results on particle production in hadronic collisions at the LHC, from proton-proton (pp) to nucleus-nucleus (AA), challenge the traditional paradigm of hadronization as a universal late-time process which can be factorized from the partonic description of the rest of the event. If the violation of this description in nuclear collisions has been accepted for long -- with several hadronic observables finding a natural interpretation assuming some form of recombination of partons from a deconfined medium -- this same occurrence came as a surprise in proton-proton collisions. Actually, strong indications that hadronization cannot be simply described by universal fragmentation fractions/functions were already found in fixed-target experiments, but limited to specific kinematic regions close to the beam rapidity, so that a complete change of paradigm did not look necessary. Here we show that a wide set of observables finds a natural interpretation assuming that in all high-energy hadronic collisions, from pp to AA, a deconfined medium is formed, acting as a reservoir in which a parton can undergo local color neutralization (LCN) through recombination with an opposite color charge. Hadronization, belonging to the non-perturbative domain of QCD, will always, inevitably, require some amount of educated modelling. However, some commong features to the various proposed model in the literature can be identified, which look necessary in order to describe the most recent data. Here we decide to focus on heavy-flavor (HF) production, since in this case the origin of at least one of the consituent quarks of the final hadron is well known and attributed to an initial hard partonic process.