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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 ?. Plasma. In normal matter

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basic question
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.

2 kinds of plasma

Plasma

In normal matter

Charge is bounded

Nor-

mal

Mat-

ter

T - ρplot

Colour is confined

Plasma

Normal

Matter

2 kinds of plasma
  • EM Plasma
  • QG Plasma

In Plasma

Charge and Colour

can move freely

em plasma
EM Plasma

Definition:

Consists of a collection of free-moving electrons and ions

Ions and Electrons move independently.

some examples of em plasma
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

Some of these plasmas are in or near thermal equilibrium, but some are not.

No (local) equilibrium is demanded

for a plasma.

slide9

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
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
The Definition of QGP

The Prevalent Definition

Should be changed into:

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.

hot and dense

slide12

Should be changed into:

  • High density: є>> єC
  • 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
  • X-N Wang’s Criteria:
  • Multiple scattering (interaction)
  • between partons (collective behavior)
slide13

Question 3: Has Quark DoF been observed yet?

or

Has Color Deconfinement been observed yet?

slide14

Direct Evidence v2 scaling

The n’s here count the number of quarks that flowed.

Parton recombination Partonic degrees of freedom

V2 scaling tells us that they are the constituent quarks that started to flow at the early stage of collision.

Constituent Quark Degree of Freedom

slide15

Some model says that originally the current quarks flow, and they recombine into constituent quarks before hadronization.

n >>3

If this were the case, then all the flowing quarks would contributeto v2 and the numbers of quarks in baryon and meson would not be 3 and 2 any more. The scaling breaks down.

questions
Questions
  • Are they really the constituent quarks that flow ?
  • Is it the constituent quark DoF that shows upat the early stage of collision?
  • What kind of vacuum is that?

We still cannot say for sure that

Quark DoF has been observed.

never forget that our ultimate goal in doing relativ heavy ion coll is to
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.

slide19

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

a model independent evidence of such a state of matter would be a great discovery it would mean
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
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.