Forward-Backward Correlations in Heavy Ion Collisions

Aaron Swindell, Morehouse CollegeREU Cyclotron 2006, Texas A&M UniversityAdvisor: Dr. Che-Ming Ko

Quantum Chromodynamics (QCD)

Utilized to strong interactions Standard model:

Quarks and Gluons Color charge (Red, Blue, and Green) Six flavors (up, down, charm, strange, top, bottom) SU(3) gauge group has 8 gauge bosons (gluon)

QCD Lagrangian F=gluon field tensor Ψ=Quark field D=covariant derivative

Pertubative QCD Running coupling:

Q=momentum transfer asymptotic freedom

Length scale converges Quark-Gluon Plasma

)1()2()3( USUSU

)(

4

1mDiFFL

M

QbQ

S

SS

log2

1 0

QCD Matter (Quark Matter)

Phase Diagram

http://www.pparc.ac.uk/frontiers/current/feature4.asp

QCD Matter (cont.)

Experimental Heavy-Ion Collisions (CERN, BNL, etc.)

Lorentz-contracted Nuclei Hard Parton collisions/Jet Interactions Parton Cascade/QGP Hadron Phase

Quark-Gluon Plasma (QGP)

Cosmic “soup” of almost-free quarks and gluons

Lattice-Gauge Theory Used at low baryon densities & high

temperatures Predicts QGP transition at MeVTtrans 170

QGP (Experimental)

Collisions of large nuclei Au+Au, Pb+Pb @ BNL & CERN =200 GeV, 5.5 TeV respectively

“Fireball” Main Observations

EM observables: photon(2-4 GeV) and dilepton enhancement

Strangeness: strangeness enhancement Kinetic observable: elliptic flow Hard probes: jet quenching, J/ψ suppression Correlation: HBT Interferometry, fluctuations

NNs

Theoretical Models

Thermal Yield of various particles, ratios

Hydrodynamic Behavior of low particles, elliptic

flow Transport

Treat chemical/thermal freeze-out dynamically

HBT Interferometry of hadrons

Tp

A Multiphase Transport model (AMPT)

Describes collisions ranging from p+A to A+A systems

RHIC =200 GeV LHC (future) =5.5 TeV HIJING (Heavy Ion Jet Interaction

Generator) Initial conditions

ZPC (Zhang’s Parton Cascade) Lund string fragmentation/Quark

coalescence ART (A Relativistic Transport)

NNs

NNs

AMPT (cont.)

Default model (v1.11) String melting (v2.11)

Forward-Backward Multiplicity Correlations using AMPT

Experimental collisions produce clusters of correlating partons

Au+Au collisions = 200 GeV 0-20% central

Event-wise observable (comparison)

Measure the variance

NNs

BF

BF

NN

NNC

22 CCC

Preliminary DataNucl-ex/0603026

Rapidity Distributions

Variance

Variance (cont.)

Analysis

Evolution of hadrons in collisions is of much importance for fluctuations (the results from HIJING are much higher than from the AMPT model)

Partonic cascade and hadronic evolution have similar effects on fluctuations

The difference in magnitude between AMPT calculations and experimental data indicates that there may exist clusters of correlated particles in heavy ion collisions (clusters aren’t made in AMPT)

L. J. Shi and S. Jeon, Phys. C72, 034904 (2005)

Acknowledgements

Cyclotron Institute Dr. Ko, Dr. Liu, Dr. Zhang NSF DOE Fellow REU Participants