Constraints on rapidity-dependent initial conditions from charged particle pseudorapidity densities and two-particle correlations

TL;DR

This paper investigates the three-dimensional initial state of quark-gluon plasma in heavy-ion collisions by using rapidity-dependent measurements and Bayesian methods to constrain initial conditions, improving understanding of the early collision dynamics.

Contribution

It introduces a cumulant-generating function to model rapidity dependence and applies Bayesian optimization to refine initial condition parameters from experimental data.

Findings

Optimized initial conditions match experimental pseudorapidity densities

Model reproduces two-particle rapidity correlations

Provides constraints on rapidity-dependent initial state models

Abstract

We study the initial three-dimensional spatial configuration of the quark-gluon plasma produced in relativistic heavy-ion collisions using centrality and rapidity-dependent measurements of charged particle pseudorapidity densities and two-particle correlations. A cumulant-generating function is used to parametrize the rapidity dependence of local entropy deposition and extend arbitrary boost-invariant initial conditions to nonzero beam rapidities. The model is compared to p+Pb and Pb+Pb single-particle distributions and systematically optimized using Bayesian parameter estimation to extract high-probability initial condition parameters. The optimized initial conditions are then compared to a number of experimental observables including two-particle rapidity correlations, the rapidity dependence of anisotropic flow, and event-plane decorrelations.