Forward-Backward Correlations in Relativistic Heavy Ion Collisions

Aaron Swindell, Morehouse College REU 2006: Cyclotron Institute, Texas A&M University Mentor: Che-Ming Ko

Quantum Chromodynamics (QCD)

QCD is the theory of the strong nuclear interaction, the fundamental force describing the activities of quarks and gluons found inside of protons and neutrons (also known as nucleons).

It’s well known for having two very peculiar properties,

confinement

and

asymptotic freedom

.

•Quarks and gluons are the fundamental particles of nature that combine in various ways to form mesons and baryons, each with their own distinct properties

–Color (charge)-

Red,

Blue, Green, and anti-colors for each –Flavor- Up, Down, Charm, Strange, Top, Bottom, and anti flavors for each

•QCD Lagrangian

L

  1 4

F



F

   (

i

 

D

 

m

)  •Pertubative QCD (pQCD), a method based on asymptotic freedom, allows QCD to be accurately tested in experiments .

QCD Matter

Quark matter refers to any phase of matter whose degrees of freedom involve quarks and gluons, which have to occur at extreme conditions. Naturally, this type of matter is believed to exist at the time of the Big Bang (Quark-Gluon Plasma) and in neutron (compact) stars. Experimentally, scientists can produce small instances, that are comparable to that of the µs-old universe, by colliding heavy nuclei at relativistic energies. Sophisticated equipment, such as the Relativistic Heavy Ion Collider (RHIC) at BNL and the future Large Hadron Collider (LHC) at CERN (Switzerland/France), is employed for such experiments.

A Multiphase Transport model (AMPT)

Default model (v1.11) String melting (v2.11) •Describes collisions ranging from

p+A to A+A systems

•

RHIC

s NN

•

HIJING (Heavy Ion Jet Interaction Generator)- Initial parameters

•

ZPC (Z hang’s Parton Cascade)

•

Lund string fragmentation/Quark coalescence

•

ART (A Relativistic Transport)

•

Observables

•

Rapidity distributions

•

Particle ratios

•

Transverse Momentum Spectra

•

Elliptic Flow

Acknowledgements

•Cyclotron Institute •Che-Ming Ko, Wei Liu, Benwei Zhang •Trent Strong •NSF •DOE

Multiplicity Correlations at RHIC Energies

The AMPT model was used to simulate the integrated charged-particle multiplicities in order to study the correlation properties of particle production in Au+Au collisions over an even distribution. After a suitable number of events, the AMPT yielded particle production that was comparable to that found by the PHOBOS detector at RHIC, and was used to calculate the event-wise observable

C

 

N F N F

 

N B N B

 For particles detected in the forward and backward rapidities, C was  2 

C

  2 characteristics (e.g. centrality)

Results

Average Rapidity Distributions 

Conclusions

•

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 has minimal effects on fluctuations (in both the default and string melting models)

•

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)