Collective interaction of QCD strings and early stages of high-multiplicity pA collisions

We study the early stages of "central" pA and peripheral AA collisions. Several observables indicate that at a sufficiently large number of participant nucleons the system undergoes a transition into a new "explosive" regime. By defining a string-string interaction through the σ meson exchange and performing molecular dynamics simulation, we argue that one should expect a strong collective implosion of the multistring "spaghetti" state, creating significant compression of the system in the transverse plane. Another consequence is the collectivization of the "σ clouds" of all strings into a chirally symmetric fireball. We find that these effects happen provided the number of strings Ns>30 or so, as only such a number can compensate a small σ-string coupling. These findings should help us to understand the subsequent explosive behavior observed for the particle multiplicities roughly corresponding to this number of strings.