Phenomenology of baryon dynamics with directed flow in relativistic heavy-ion collisions

TL;DR

This thesis develops a hydrodynamic model incorporating a new initial baryon distribution to explain directed flow and baryon-antibaryon splitting in heavy-ion collisions, providing insights into baryon stopping, diffusion, and electromagnetic effects.

Contribution

It introduces a novel initial baryon deposition ansatz within a hydrodynamic framework, successfully describing $v_1$ observables and estimating the baryon diffusion coefficient in QCD matter.

Findings

Successfully describes rapidity-odd $v_1$ and baryon-antibaryon splitting across energies.

Shows background baryon stopping effects influence electromagnetic field measurements.

Provides the first estimate of the baryon diffusion coefficient in QCD matter.

Abstract

This thesis aims to elucidate the role of initial baryon stopping and its diffusion in heavy-ion collisions (HIC) using hydrodynamic model. In this regard, we have studied the observable-directed flow ($v_1$) of identified hadrons, particularly the $v_1$ of baryons and antibaryons, as well as the splitting observed between them in detail. We propose a new ansatz for the initial baryon distribution. By employing this initial baryon deposition model alongside a tilted energy distribution as inputs to a hybrid framework, we successfully describe the rapidity-odd $v_1$ of identified hadrons, including the elusive baryon-antibaryon splitting of $v_1$ across a wide range of $\sqrt{s_{NN}}$. Our model, incorporating baryon stopping and it's subsequent diffusion within a relativistic hydrodynamic framework and employing a crossover equation of state derived from lattice QCD calculations, establishes a non-critical baryonic baseline. Moreover, we demonstrate that recent STAR measurements of the centrality and system-size dependence of $v_1$ splitting between oppositely charged hadrons-attributed to electromagnetic field effects-are significantly influenced by background contributions from baryon stopping and its diffusion. Furthermore, we show that the rapidity dependence of the splitting of the rapidity-even component of $v_1$ between $p$ and $\bar{p}$ is highly sensitive to the initial baryon deposition scheme. If measured experimentally, this could constraint the rapidity dependence of the initial baryon deposition profile. Moreover, it could offer valuable phenomenological insights into the baryon junction picture and help refine constraints on the baryon diffusion coefficient of the medium. Notably, utilizing this phenomenologically successful baryon deposition model, we present the first estimation of the baryon diffusion coefficient for the strongly interacting QCD matter created in HIC.