Nuclear/Particle Theory Group: The Physics of the QGP

Hot and Dense QCD:
The Physics of the Quark-Gluon-Plasma


Current and Former Group Members


Introduction into Quark-Gluon-Plasma Physics:

Hadronic matter - matter susceptible to the strong interaction force - is described by quantum-chromo-dynamics (QCD). The basic constituents of QCD are quarks which interact through the exchange of gluons. It is believed that shortly after the creation of the universe in the Big Bang all matter was in a state called the Quark Gluon Plasma (QGP). Due to the rapid expansion of the universe, this plasma went through a phase transition to form hadrons - most importantly nucleons - which constitute the building blocks of (nuclear) matter as we know it today. The investigation of QGP properties, such as its equation of state, will improve our understanding of the development of the early universe and the behavior of QCD under extreme conditions.

Timeline of the history of the Universe and the evolution of matter from the Big Bang to the present.

The existence of a QGP can be theoretically inferred through lattice gauge simulations of QCD (see also the page on our group's activities in that sector), which provide the only rigorous method to compute the QCD equation of state. These simulations predict a phase transition of confined hadronic matter (such as protons and neutrons) to a deconfined state in which hadrons are dissolved into quarks and gluons. Further information, however, such as the critical temperature and energy-density for that phase-transition, depend crucially on the parameters of the simulation and the extrapolation from the discretized quantities on the lattice to the continuum of the real world.

Conditions for creating this highly excited state of primordial matter under controlled laboratory conditions using relativistic heavy ion collisions are currently being provided by the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory . RHIC collides gold nuclei at center of mass energies of 130 GeV and 200 GeV per nucleon-nucleon pair and thus creates a state of matter at the highest temperatures and densities possible in a laboratory environment. Experiments at RHIC have yielded many interesting and sometimes surprising results, which have not yet been fully evaluated or understood by theory.

Two views of one of the first full-energy collisions between gold ions at Brookhaven Lab's Relativistic Heavy Ion Collider, as captured by the Solenoidal Tracker At RHIC (STAR) detector. The tracks indicate the paths taken by thousands of subatomic particles produced in the collisions as they pass through the STAR Time Projection Chamber, a large, 3-D digitial camera.

The central problem in the study of the QGP is that the deconfined quanta of a QGP are not directly observable due to the fundamental confining property of the physical QCD vacuum. If we could see free quarks and gluons (as in ordinary plasmas) it would be trivial to verify the QCD prediction of the QGP state. However, nature chooses to hide those constituents within the confines of color neutral composite many body systems - hadrons. One of the main tasks in relativistic heavy-ion research is to find clear and unambiguous connections between the transient quark gluon plasma state and the observable hadronic final state.

QGP Research at Duke

Our group has a longstanding tradition in QGP related research. We are active in the following areas:
  • Heavy-Ion Phenomenology:
    • Hadronization via parton recombination and fragmentation
    • the phenomenology of jet quenching
    • charge and baryon number fluctuations
    • balance functions
  • Hydrodynamical description of Relativistic Heavy-Ion Collisions
  • Microscopic transport models
    • Parton Cascade Models
    • Ultra-Relativistic Quantum Molecular Dynamics
    • Hybrid Macro+Micro transport approaches
An autogenerated list of recent publications (from 1998 onwards) by the Duke Nuclear/High Energy Theory Group on QGP related topics can be found here.