Baryon inhomogeneities driven charge dependent directed flow in heavy ion collisions

TL;DR

This paper shows that baryon inhomogeneities can explain the charge-dependent directed flow splitting observed in heavy ion collisions without electromagnetic effects, highlighting the role of baryon current responses to initial inhomogeneities.

Contribution

It introduces a relativistic dissipative fluid dynamic model with baryon diffusion and realistic initial conditions that accounts for the observed charge-dependent flow splitting involving baryons.

Findings

Baryon inhomogeneities significantly contribute to charge-dependent directed flow.

The model reproduces observed $ ext{v}_1$ splitting for baryons and anti-baryons.

Electromagnetic effects are not necessary to explain the data.

Abstract

Electromagnetic field in heavy ion collisions are expected to cause charge dependent directed flow splitting ($\Delta v_1$). Such charge dependent $\Delta v_1$ has been observed by the STAR collaboration. We demonstrate that relativistic dissipative fluid dynamic simulations with baryon diffusion that include realistic model of baryon stopping in the initial condition and no contribution from electromagnetic field describe the measured $\Delta v_1$ for observables involving baryons and anti-baryons. This suggests strong background contribution from baryon current as a response to initial state baryon inhomogeneities to such charge dependent $\Delta v_1$ involving baryons and anti-baryons. Our current model calculations that only account for the evolution of the baryon charge and not electric charge and strangeness miss the observed $\Delta v_1$ of mesons leaving their interpretation open.