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

Abstract

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 (${p}_{T}$) 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 $\mathrm{\ensuremath{\Omega}}$ baryons to charged pions as inputs, we extract the fraction of core and corona components in $p+p$ collisions at $\sqrt{s}=7\phantom{\rule{0.16em}{0ex}}\mathrm{TeV}$ and $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{{s}_{NN}}=2.76\phantom{\rule{0.16em}{0ex}}\mathrm{TeV}$. We find core contribution overtakes corona contribution as increasing multiplicity above ${\ensuremath{\langle}d{N}_{\mathrm{ch}}/d\ensuremath{\eta}\ensuremath{\rangle}}_{|\ensuremath{\eta}|<0.5}\ensuremath{\approx}18$ 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 $\ensuremath{\approx}20%$ below ${p}_{T}\ensuremath{\approx}1$ GeV even in minimum bias $\mathrm{Pb}+\mathrm{Pb}$ collisions. We find that the corona contribution at low ${p}_{T}$ gives $\ensuremath{\approx}15\ensuremath{-}30%$ correction on ${v}_{2}{2}$ at ${N}_{\mathrm{ch}}\ensuremath{\lesssim}370$. This raises a problem in conventional hydrodynamic analyses in which low-${p}_{T}$ 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.

Topics & Concepts