New approach to initializing hydrodynamic fields and mini-jet propagation in quark-gluon fluids

Abstract

We propose a new approach to initialize the hydrodynamic fields such as energy density distributions and four flow velocity fields in hydrodynamic modeling of high-energy nuclear collisions at the collider energies. Instead of matching the energy-momentum tensor or putting the initial conditions of quark-gluon fluids at a fixed initial time, we utilize a framework of relativistic hydrodynamic equations with source terms to describe the initial stage. Putting the energy and momentum loss rate of the initial partons into the source terms, we obtain hydrodynamic initial conditions dynamically. The resultant initial profile of the quark-gluon fluid looks highly bumpy as seen in the conventional event-by-event initial conditions. In addition, initial random flow velocity fields also are generated as a consequence of momentum deposition from the initial partons. We regard the partons that survive after the dynamical initialization process as the mini-jets and find sizable effects of both mini-jet propagation in the quark-gluon fluids and initial random transverse flow on the final momentum spectra and anisotropic flow observables. We perform event-by-event (3 + 1)-dimensional ideal hydrodynamic simulations with this new framework that enables us to describe the hydrodynamic bulk collectivity, parton energy loss, and interplay among them in a unified manner.

Unified description of hadron yield ratios from dynamical core-corona initialization

“…1 Under this framework, the initial condition of the QGP fluids is obtained via energy-momentum deposition from the partons/strings/fields generated just after the collision. As extension of the dynamical initialization description for QGP fluids generation from initially produced partons [47][48][49][50], we introduced the dependence on initial parton densities in the dynamical initialization [50], which we call the "dynamical core-corona initialization (DCCI) model" in this paper. Given the various definitions of the core and the corona in the literature [41][42][43][44][45][46], we here define them explicitly as follows: The core represents the fluids under local thermal and chemical equilibrium, while the corona represents the system composed of non-equilibrated partons traversing the fluids or the vacuum.…”

Equilibration and baryon densities attainable in relativistic heavy-ion collisions

“…The main part of the hydro models [17][18][19][20][21][22][23], that are designed for describing evolution of the baryon-rich matter, takes their initial conditions from third-party kinetic codes. Unlike those hybrid hydro models, the 3FD model [12] takes into account finite stopping power of nuclear matter right within the 3FD evolution.…”

“…Thus, the 3FD approximation is a minimal way to simulate the earlystage nonequilibrium at high collision energies. Similar concepts were used in recently developed hybrid models [20][21][22][23]. Unlike the 3FD, these hybrid models deal with a single equilibrated fluid that however does not involve all the matter of colliding nuclei.…”

Rapidity Decorrelation from Hydrodynamic Fluctuations and Initial Fluctuations

“…The model is extended in the longitudinal direction by using an general purpose event generator PYTHIA. To account for heavy ion collisions, we accumulate inelastic p+p events in PYTHIA by the number of binary collisions estimated above and accept the produced particles using rapidity Y and transverse momentum p T dependent acceptance function w(Y, p T ) [4,5]…”