Post on 14-Jan-2016
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A Multi-Phase Transport Modelfor High Energy Heavy Ion Collisions
NSSTC Marshall Space Flight Center August 7, 2003
Zi-wei LinThe Ohio State University
in collaboration with C.M. Ko (TAMU), Bao-An Li (ASU),
Subrata Pal (MSU) and Bin Zhang (ASU)
Outline
Why do we need a transport model?
Structure of a multi-phase transport (AMPT) model
Selected results at high energies from AMPT
Summary
1
Major Experiments
High Energy Heavy IonMachines s (AGeV) Main Beam
CERN-SPS (past) 8-17 Pb+PbBNL-RHIC (now) ~20-200 Au+AuCERN-LHC (future) up to 5500 Pb+Pb
RHIC (Relativistic Heavy Ion Collider) at Brookhaven National Laboratory
Au+Au collisions up to 200AGeV
~ 2.5 6 20 GeV/fm3SPS RHIC200 LHC
>>critical energy densityfor QCD phase transitionproper formation
time, take 1fm/c
High energy density/temperature ~ universe 1ms after the Big Bang
Study properties of high density partonic and hadronic matter
How high is the initial energy density?
nuclear radius
A general modelfor high energy heavy ion collisions
needs:
●Initial condition for particle and energy production
●Parton stage with EoS
●hadronization/phase transition
●hadronic interactions
some options:
soft+hard model, saturation models, ...
parton cascade, hydrodynamics, ...
string fragmentation, coalescence, statistical hadronization, ...
hadron cascade (ART, RQMD, ...)
A Multi-Phase Transport (AMPT) model includes the above green ingredients
Advantages of a transport model
Can address dynamics at non-equilibrium Chemical and kinetic freezeouts are generated self-consistently
Allows numerical studies beyond limits of analytical methods
Can learn about details of the evolution of many-body systems
HIJING (Heavy Ion Jet Interaction Generator) minijet partons(hard)
+strings(soft)
ZPC (Zhang's Parton Cascade)
Lund fragmentation to hadrons
ART (A Relativistic Transport model for hadrons)
A+B
Strong-decay all resonances for final particle spectra
Structure of AMPT model Zhang et al, PRC61, PRC65;
Lin et al, PRC64, NPA698,
PRC65, PRL89.
Wang&Gyulassy, PRD43,44,45
Zhang, CompPhysComm82
Li&Ko, PRC52
Parton freezeout
Generate parton space-time
Main Ingredients
HIJING version 1.383
ZPC 2-2 parton processes: gg-gg, gg-qqbar, gq-gq, ...
Hadronization Lund string fragmentation/quark coalescence
ART hadron interactions including:
Parton Cascade
To study dynamics of strong interactions in a QCD matter.
The equation of motion may be written as
For 2-2 interacitons:ZPC (Zhang's Parton Cascade) solves theseBoltzmann equations by the cascade method:
2 particles scatter if their distance <
Parton cross sections
From leading-order QCD:
Use a medium-generated screening mass to regulate the divergence:
Causality violation and a solution
●Causality problem:Classical cascade breaks down when Mean-Free-Path < Interaction length
•A solution: particle subdivision
unchanged
Zhang,Gyulassy&Pang, PRC58
Lund String Fragmentation
Assume:production positions at a constant proper time,left-right symmetry (ordering of Vn just represent different Lorentz frames)
Lund symmetric splitting function
Andersson et al,
PhysRep 97; ZPC20
percentage of light-cone momentum of the produced parton
The Schwinger Mechanism: •particle production from an external field via tunneling
Potential energy=
•Production probability
•Strangeness suppression:~0.3
the string tension
The Schwinger Mechanism Lund String Model
Mean Momentum square:
Hadron Cascade
Based on ART Li&Ko, PRC52
Kbar interactions added Song,Li&Ko, NPA646
NNbar annhilation, K0 productions Zhang et al, PRC61
BBbar-mesons, explicit K*, Lin et al, PRC64, NPA698
interactions Lin&Ko,PRC65Lin,Ko&Pal, PRL89
Multi-strange () interactions Pal,Ko&Lin, nucl/0106073
interactions Pal,Ko&Lin, NPA707
Meson-Meson channels
SU(2):
with strangeness:
Example: meson cross sections Pal,Ko&Lin, NPA707
Meson-Baryon channels
Example: K- baryon cross sections Pal,Ko&Lin, nucl/0106073
Pion multiplicity distribution from ppbar annihilation:
Ko&Yuan, PLB192
Baryon-AntiBaryon channels
Baryon-Baryon channels
Example:
130AGeV Central AuAu Event from AMPT
In default HIJING, a=0.5, b=0.9/GeV2
need changes:a=2.2, b=0.5/GeV2
a&b in the Lund splitting function:
~same
Lin et al, PRC64, NPA698
SPS: Pb+Pb collisions at 17AGeV
m spectra at SPS
Final-state rescatteringsin AMPT modelincrease mslopeof heavy particles
Lin et al, NPA698
Results at RHIC Energies (b=0-3fm Au+Au)
Lin et al, PRC64,
NPA698
Particle yields and ratio: energy dependence
Rapid increase for pbar/p,
baryon-antibaryon symmetric ~ early universe
Lin et al, PRC64
BRAHMS, PLB523
AMPT versus RHIC data:Pseudo-rapidity distribution at 130AGeV
AMPT versus RHIC data:Ratios of 200AGeV/130AGeV:
BRAHMS, PRL88
AMPT
QCD saturation model
More Studies with AMPT
Azimuthal momentum asymmetry Lin&Ko,PRC65
Multi-strange baryon () enhancement Pal,Ko&Lin, nucl/0106073
meson puzzle Pal,Ko&Lin, NPA707
J/ production/suppression Zhang et al, PRC62, PRC65
- interferometry/HBT Lin,Ko&Pal, PRL89
A Multi-Phase Transport (AMPT) model
is constructed for high energy heavy ion collisions
including both partonic and hadronic interactions
Hadronic/partonic interactions are important
for particle multiplicities and momentum spectra
AMPT model provides a valuable tool to study heavy ion collisions
Summary
Slides of this talk available at http://nt3.phys.columbia.edu/people/zlin/PUBLICATIONS