# Presentation: 079965

## Search for the Quark Gluon Plasma:   A Status Report

- J. Nagle
- University of Colorado

## Phase Diagram of Nuclear Matter

## What is the Quark Gluon Plasma?

- Lattice QCD reveals a rapid increase in the degrees of freedom associated with the deconfinement of quarks and gluons.

- Screening of long-range confining potential

- Transition point:
-     T ~ 170 MeV
-  ~   1.0 GeV/fm3

- F. Karsch, Prog. Theor. Phys. Suppl. 153, 106 (2004)

## Coupling Strength

- Is the Quark Gluon Plasma a free gas of nearly massless quarks and gluons?

## Phase Transition Order?

**Light Quark Mass**

**Strange Quark Mass**

**? Physical **
**    ****Point**

## Early Universe

## The Experiment

-  Relativistic Heavy Ion Collider online since 2000.
-  Design Gold Gold energy and luminosity achieved.
-  All experiments successfully taking data
-  Polarized proton proton (spin) program also underway

## In the Laboratory

- 10,000 gluons, quarks, and antiquarks
- from the nuclear wavefunctions
- are made physical in the laboratory !

## Slide 9

## Energy 

- Out of 39.4 TeV maximum energy, at least _26 TeV_ is made available for heating the fireball.
- Transverse energy indicates initial energy density well above the transition value.

- Energy

## Collective Motion

-  In non central collisions, large initial spatial anisotropy
-  The degree to which this translated into momentum space is an excellent measure of the pressure

## Hydrodynamic Behavior

- Equilibration time _t=0.6 fm/c_ and ___=20 GeV/fm__3_

- v2

- pT (GeV)

- Starting with initial conditions, hydrodynamic calculations with zero viscosity reasonably describe the data.

## Near-Perfect Fluid

- Critical goal to put the QGP data point on this plot

- ?

- Motivated by AdS/CFT calculated lower viscosity bound

## Microscopic Picture to Hydrodynamics

- Clearly the system is not a hadron gas.  Not surprising.

## Microscopic Picture to Hydrodynamics

- _Clearly this is not a perturbative QGP.  Not surprising._

## Plasma Instabilities

- Scaled Field Energy Density

- Exponential growth of color fields due to instabilities.
- Very rapid isotropization.
- Rapid thermalization is still a mystery, but with exciting possible explanations.

## Hadronization

- Even the heavy  show large flow.
- At high pT, they deviate from hydrodynamics.

## Probing the Medium

## Color Probes of the Medium

- If the plasma is dense enough we expect the quark or gluon to be swallowed up.

## Very Opaque Medium

- Quarks and gluons disappear into medium, except consistent with surface emission.

- Survival Probability

**Photons**

******0****, ******** from quark and gluon jets**

## Jet Quenching!

- Azimuthal Angular Correlations

## Reaction of the Medium

- Reflected Distribution

## Heavy Quarks

- Naive assumption is that heavy quarks are too massive to quickly thermalize in medium.

- If interactions are strong enough, prediction is for large push of charm to low pT and large v2 anisotropy.

- Suppression Factor

## Charm Results

- Key measure to help pin down viscosity.

- Single non-photonic electrons tell us about D and B mesons.

## Heavy Quarkonia

- But not as much as expected if we have complete color screening.

- We expect a suppression of bound states due to color screening in the
- Quark Gluon Plasma.

## Resolving the Puzzle

- Recent Lattice QCD results
- indicate J/ spectral function may persist up to 3 Tc.
- Temperature Bound < 3 Tc (?)

- J/

## Thermal Radiation?

- New method for heavy ion reactions of measuring virtual photons allows one to subtract away 0 and  decay contributions.
- First results show indication of photon radiation above NLO pQCD initial scattering contribution.
- Working towards a temperature determination.

## NA60 and Low Mass Pairs

- Low mass dileptons give us a probe of the interactions in the hot dense early phase.

- e-

- e+

- Key next measurement at RHIC

## Conclusions

- the Quark Gluon Plasma!
- Now we have many exciting
- properties to understand...
-  low viscosity
-  rapid equilibration
-  novel hadron formation mechanisms
-  jet quenching and medium reaction
-  temperature determination
-  degrees of freedom

## Fight the Future

- Very significant cuts in basic research in the Department of Energy Office of Science are being proposed.

- It is hard for me to imagine a world where we stop asking the big questions or stop trying to answer them.

## Extra Slides

## Signatures of the QGP

## Smooth Cross Over?

- Observables show a smooth energy dependence.

- Source Emission Size