The VII-th International Conference on the Initial Stages of High-Energy Nuclear Collisions : Initial Stages 2023

Probing the initial condition with the directed flow of light flavor hadrons

Not scheduled

20m

Copenhagen

Poster Collective dynamics from small to large systems

Speaker

Mr Tribhuban Parida 1820502

Description

The rapidity dependent directed flow, $v_1(y)$ of identified hadrons as well as the observed $v_1(y)-$splitting between baryon and anti-baryon is very sensitive to the initial three-dimensional distribution of energy and net-baryon density inside the fireball. Therefore, a suitable initial condition that can provide a consistent description of $v_1(y)$ across beam energies could serve as a better input to study the dynamics of conserved charges in hydrodynamic models. In this regard, we have proposed a two-component baryon deposition scheme where the initial baryon gradient in the transverse plane is determined by the contributions from both participant and binary collision sources. Along with that, considering the asymmetric deposition of matter and baryon density along rapidity by forward and backward moving participants, we obtain tilted profiles of both energy and net-baryon in the reaction plane, albeit the tilts are different. Taking the initial profile as an input of a hybrid framework (hydrodynamics + hadronic transport), we are able to capture the measured $v_1(y)$ of light flavor mesons ($\pi^{\pm}, K^{\pm}, \phi$), baryons ($p$, $\bar{p}$, $\Lambda$, $\bar{\Lambda}$) including the elusive particle-antiparticle $v_1$ split across beam energies ranging from 7.7 GeV to 200 GeV.

Recently, the STAR collaboration has presented preliminary results on the splitting of $v_1(y)-$slope ($\Delta (dv_1/ dy)$) between positively and negatively charged hadrons as a function of centrality. The observed sign change of $\Delta (dv_1/ dy)$ with centrality is proposed as a signature of the electromagnetic field. However, we demonstrate that the measured sign change can be described with our model of baryon stopping without considering any electromagnetic field effects. This suggests that baryon stopping in the initial stage serves large background to such signals of the electromagnetic field and underlines the need of a comprehensive understanding of the baryon stopping physics.