A new study proposes the existence of two critical phase transitions in the matter produced in heavy-ion (A-A) and proton-proton (pp) collisions at the CERN Large Hadron Collider (LHC). These transitions are associated with the percolation of color strings and the percolation of their hard cores, which would explain the observed fluid-like behavior of the matter generated in these collisions.

The first transition, at a temperature of approximately 160 MeV, is related to the restoration of chiral symmetry and partial deconfinement of quarks and gluons. The second, at about 220 MeV, would mark the transition from a strongly interacting quark-gluon plasma, which behaves as a fluid, to a quasi-free gas of quarks and gluons. This interpretation is supported by recent observations of a sudden increase in the degrees of freedom above the deconfinement temperature in pp and A-A collisions.

The model suggests that the color strings, formed between the constituents of the projectile and target, possess a "hard core" that generates repulsion between them. The percolation of these strings, and subsequently that of their hard cores, defines the two critical densities that translate into the transition temperatures. This framework offers a physical explanation for the fluid nature of QCD matter observed in LHC experiments.