Monte Carlo event generator for initial conditions of conserved charges in nuclear geometry

Abstract

At top collider energies where baryon stopping is negligible, the initial state of heavy ion collisions is overall charge neutral and predominantly composed of gluons. Nevertheless, there can also be significant local fluctuations of the baryon number, strangeness, and electric charge densities about zero, perturbatively corresponding to the production of quark/antiquark pairs. These previously ignored local charge fluctuations can permit the study of charge diffusion in the quark-gluon plasma (QGP), even at top collider energies. In this paper we present a new model denoted iccing (Initial Conserved Charges in Nuclear Geometry) which can reconstruct the initial conditions of conserved charges in the QGP by sampling a (g → q q) splitting probability over the initial energy density. We find that the new charge distributions generally differ from the bulk energy density; in particular, the strangeness distribution is significantly more eccentric than standard bulk observables and appears to be associated with the geometry of hot spots in the initial state. The new information provided by these conserved charges opens the door to studying a wealth of new charge-and flavor-dependent correlations in the initial state and ultimately the charge transport parameters of the QGP.

Initializing BSQ with Open-Source ICCING

“…A distribution is sampled to determine the fraction of the available energy that will be the gluon. Then a Monte Carlo sampling of the quark flavor ratios provided in [38] is used to determine whether the gluon will split into a quark antiquark pair and what its flavor would be if this were the case. Another sampling is done to determine both the distance between the two quarks and the fraction of energy that is shared by each (the probability distributions for this process are beyond the scope of this work and are detailed in Ref.…”

“…Another sampling is done to determine both the distance between the two quarks and the fraction of energy that is shared by each (the probability distributions for this process are beyond the scope of this work and are detailed in Ref. [38]). Finally, the energy, baryon, strange, and charge densities of the quark and antiquark are distributed in the output density grids and if the gluon did not undergo a splitting, its energy is copied over without modification.…”

“…As a result of redistributing the energy density from the g → q q splitting, the energy density profile is somewhat modified, including visible artifacts associated with the model implementation. Taken from [38].…”

“…This relationship is not perfect and in peripheral collisions non-linear corrections to the hydrodynamic response can become significant [51][52][53]. Taken from [38].…”

“…This work focuses on the implementation of the former as a Monte Carlo algorithm that takes any initial condition, that can be described as an energy density, and samples the g → q q splitting probability to introduce BSQ conserved charges as quark pairs. The algorithm presented here is ICCING, Initial Conserved Charges in Nuclear Geometry, and is formulated in a modular way to allow for the selection of different choices for all theoretically dependent components, including the initial energy density in-put, the g → q q splitting probabilities, and the distribution of charge densities [38,39]. The events modified by ICCING can be read directly into hydrodynamic simulations.…”