1. Introduction Results Methods Conclusions
Vorticity in High-Energy Heavy-Ion Collisions
De-Xian Wei and Xu-Guang Huang
Department of Physics and Center for Field Theory and Particle Physics, Fudan University, Shanghai, , China
Introduction
Results
With generate approximately events with 10 fm impact parameter on Au+Au collisions at √sNN = 200 GeV. Results shows that the magnitude of the vorticity is decay with time evolution.
High-energy heavy-ion collisions operated in the Relativistic Heavy Ion Collider (RHIC) [1–2] at Brookhaven National Laboratory (BNL) and in the Large Hadron Collider (LHC) [3] at CERN have successfully created a new state of matter, the strongly interacting Quark Gluon Plasma (QGP). One of the main features of such QGP is that it reaches local thermodynamic equilibrium and its evolution can be well described by relativistic hydrodynamics. In such a vortical fluid, the spin-orbital coupling polarizes the spin of fermions (quarks and baryons) [4-5] along the direction of the vorticity.
The purpose of the present work is to give a detailed study of the vorticity field which contributed by angular momentum by using A MultiPhase Transport (AMPT) model. We will perform a study on event-by-event basis and will determine the time evolution of the vorticity field, and also calculated the polarization of Lambda hyperons.
Fig.1 Schematic view of the high energy nuclear collision.
Methods
The AMPT model is a Monte Carlo transport model for high-energy heavy ion collisions [6]. We will use the string-melting version of the AMPT model which is consist of four main stages: initial condition(given by the Heavy Ion Jet INteraction Generator (HIJING) 2.0 model[7]), parton cascade(The partonic matter evolves according to the Zhangs parton cascade (ZPC) [8]), hadronization(via a coalescence model ), and hadronic rescattering(which is based on a relativistic transport (ART) model[9]).
In peripheral collision(where take 10 fm impact parameter), one can be see that the vorticity is mainly distributed in the central rapidity region. That’s implies, polarization in the collisions is focussing on the central rapidity region. And also, we calculted the polarization of Lambda and compared to the experimental data, the meaning polarization of Lambda is sensitive to the collision energy.
To compute the vorticity, We must first define the particles velocity field which is calculated by a smearing function[10],
Where the smearing function whose functional is a Gaussian
Then, the vorticity is calculated according to
Conclusions
We perform a study on the vorticity field evolution with event-by-event simulation, and calculate the polarization of Lambda hyperons, and the results is consistent with the experimental data of Lambda polarization
We perform on the evolution of the vorticity field by a parton cascade in the AMPT model with event-by-event simulation.
The most straightforward way to detect a global polarization in relativistic nuclear collisions is focussing on Lambda hyperons. To investigate this effect, one can analysis the azimuths of the emitting proton which decay from Lambda,
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Fig.2 Schematic view of the Lambda polarization in the collision [11].