Interplay between core and corona components in high-energy nuclear collisions

We establish the updated version of dynamical core-corona initialization framework (DCCI2) as a unified description from small to large colliding systems and from low- to high-transverse-momentum (pT) regions. Using DCCI2, we investigate effects of interplay between locally equilibrated and nonequilibrated systems, in other words, core and corona components in high-energy nuclear collisions. Given experimental multiplicity distributions and yield ratios of Q baryons to charged pions as inputs, we extract the fraction of core and corona components in p + p collisions at root s = 7 TeV and Pb + Pb collisions at root sNN = 2.76 TeV. We find core contribution overtakes corona contribution as increasing multiplicity above (dNch/d eta|eta|<0.5 approximate to 18 regardless of the collision system or energy. We also see that the core contribution exceeds the corona contribution only in 0.0-0.95% multiplicity class in p + p collisions. Notably, there is a small enhancement of corona contribution with approximate to 20% below pT approximate to 1 GeV even in minimum bias Pb + Pb collisions. We find that the corona contribution at low pT gives approximate to 15-30% correction on v2{2} at Nch < 370. This raises a problem in conventional hydrodynamic analyses in which low-pT soft hadrons originate solely from core components. We finally scrutinize the roles of string fragmentation and the longitudinal expansion in the transverse energy per unit rapidity, which is crucial in initial conditions for hydrodynamics from event generators based on string models.

Automated summary

We establish an updated version of the dynamical core-corona initialization framework that provides a unified description of small to large colliding systems and low to high-transverse-momentum regions. Using this framework, we investigate the interplay between locally equilibrated and nonequilibrated systems in high-energy nuclear collisions. Based on experimental data, we extract the fraction of core and corona components in p+p and Pb+Pb collisions. The results show that the core contribution overtakes the corona contribution as the multiplicity increases, and this is observed regardless of the collision system or energy. Additionally, we find a small enhancement of corona contribution at low transverse momentum in Pb+Pb collisions, which raises concerns for conventional hydrodynamic analyses.