An Initial State with Shear in Peripheral Heavy Ion Collisions

TL;DR

This paper introduces a new initial state model for relativistic heavy ion collisions that incorporates shear and angular momentum, aligning with experimental observations of vorticity and enabling compatibility with various hydrodynamical codes.

Contribution

The paper presents a novel initial state model based on a streak-by-streak Bjorken-like solution that conserves angular momentum and includes shear, suitable for 3+1D hydrodynamic simulations.

Findings

Model satisfies conservation laws including angular momentum.

Predicts system rotation and fluid shear leading to vorticity.

Compatible with existing 3+1D hydrodynamical codes.

Abstract

In the present work we propose a new initial state model for hydrodynamic simulation of relativistic heavy ion collisions based on Bjorken-like solution applied streak by streak in the transverse plane. Previous fluid dynamical calculations in Cartesian coordinates with an initial state based on a streak by streak Yang-Mills field led for peripheral higher energy collisions to large angular momentum, initial shear flow and significant local vorticity. Recent experiments verified the existence of this vorticity via the resulting polarization of emitted $\Lambda$ and $\bar{\Lambda}$ particles. At the same time parton cascade models indicated the existence of more compact initial state configurations, which we are going to simulate in our approach. The proposed model satisfies all the conservation laws including conservation of a strong initial angular momentum which is present in non-central collisions. As a consequence of this large initial angular momentum we observe the rotation of the whole system as well as the fluid shear in the initial state, which leads to large flow vorticity. Another advantage of the proposed model is that the initial state can be given in both [t,x,y,z] and $[\tau, x, y, \eta]$ coordinates, and thus can be tested by all 3+1D hydrodynamical codes which exist in the field.