Some Questions about QGP July 2004

Basic Question Has Quark-Gluon Plasma been observed? or When and How will it be observed? The answer depends on the definition. A proper definition should catch the essential points.

Question 1: What is Plasma ?

2 kinds of plasma EM Plasma QG Plasma T - ρplot Normal Matter Nor- mal Mat- ter Plasma In normal matter Charge is bounded Colour is confined In Plasma Charge and Colour can move freely

EM Plasma Definition: Consists of a collection of free- moving electrons and ions Ions and Electrons move independently.

Some Examples of EM Plasma Tokamak plasma in action Princeton Plasma Physics Laboratory Nebula M1-67 a massive stellar wind NASA High-intensity plasma arc lamp Courtesy of OSRAM Sylvania, Danvers, MA Atmospheric Plasma Courtesy of J. Elston Litmas No (local) equilibrium is demanded for a plasma. Some of these plasmas are in or near thermal equilibrium, but some are not.

Question 2: Why RHIC ?

Workshop on BeV/n collisions of heavy ions – how and why, Bear Mountain, 1974

T.D.Lee & G. C. Wick Lee emphasized, whether the vacuum is a medium whose properties one could change; "we should investigate," he pointed out, “... by distributing high energy or high nucleon density over a relatively large volume." If in this way one could restore broken symmetries of the vacuum, then it might be possible to create abnormal dense states of nuclear matter

Our ultimate goal in doing Relativ. Heavy Ion Coll. is to Change the QCD vacuum Librate the confined quark-gluon Restore the chiral symmetry No (local) equilibrium is demanded too

The Definition of QGP A (locally) thermally equilibrated state of matter in which quarks and gluons are deconfined from hadrons, so that color degrees of freedom become manifest over nuclear, rather than merely nucleonic, volumes. The Prevalent DefinitionShould be changed into: hot and dense

X-N Wang ’ s Criteria: High density: є >> є C Large volume: V >> λ (mean-free-path) Long life-time: t >> λ Parton degrees of freedom Local thermal equilibration (interaction) approximately Debye screening of strong interaction: deconfinement Should be changed into: Multiple scattering (interaction) between partons (collective behavior)

Question 3: Has Quark DoF been observed yet? Has Color Deconfinement been observed yet? or

Direct Evidence v 2 scaling Parton recombination Partonic degrees of freedom The n’s here count the number of quarks that flowed. V 2 scaling tells us that they are the constituent quarks that started to flow at the early stage of collision. Constituent Quark Degree of Freedom

If this were the case, then all the flowing quarks would contribute to v 2 and the numbers of quarks in baryon and meson would not be 3 and 2 any more. The scaling breaks down. n >>3 Some model says that originally the current quarks flow, and they recombine into constituent quarks before hadronization.

Questions Are they really the constituent quarks that flow ? Is it the constituent quark DoF that shows up at the early stage of collision ? What kind of vacuum is that? We still cannot say for sure that Quark DoF has been observed.

Conclusion

Never forget that our ultimate goal in doing Relativ. Heavy Ion Coll. is to: Change the QCD vacuum Librate the confined quark-gluon Restore the chiral symmetry Our main effort should be concentrated in finding out direct, model-independent evidences for these 3 points.

The other properties of the produced system, e.g. thermalized or not are worthwhile investigating. But the results of this investigation do not affect the discovery or non-discovery of QGP.

Thanks!

A model-independent evidence of such a state of matter would be a great discovery. It would mean: The QCD vacuum has been successfully changed The Color Confinement has been successfully broken This discovery will become a milestone in the development of physics

Other Questions like Whether or not there is (local)equilibrium? Why there seems to be an expansion, but at the same time the volume measured by HBT is unchanged? ? can be left for further study.