Constraints on rapidity-dependent initial conditions from charged particle pseudorapidity densities and correlations at the LHC

Abstract

The initial three-dimensional entropy distribution of the quark-gluon plasma produced in relativistic heavy-ion collision is systematically studied using parametric initial conditions. We apply a cumulant generating function approach to parametrize the rapidity dependence of local entropy deposition and extend the boost-invariant initial condition model TRENTo to include longitudinal structure. Two different parametrizations are tested and their parameters optimized by comparing to centrality dependent charged particle pseudorapidity densities of p+Pb (5.02A TeV) and Pb+Pb (2.76A TeV) using Bayesian inference. Successful parametrizations are then selected based on their ability to describe two-particle psuedorapidity correlations. Finally, we predict the pseudorapidity dependent flows and event-plane decorrelations using the optimized initial conditions and a 3+1D hybrid hydro+micro model.