# Presentation: 211972

## High Energy Nuclear Physics and the Nature of Matter

- Outstanding questions about strongly interacting matter:
- How does matter behave at very high temperature and/or density?
- What is the nature of gluonic matter?
- How does this gluonic matter appear inside of strongly interacting particles?
- How are spin and baryon number distributed inside of nucleons?
- RHIC addresses all of these.

- Partially resolved issues:
- Spectra, matrix elements and thermodynamics from first principles computation in QCD
- Can QCD be turned into a precision science?

## What is the behavior of strongly interacting matter at high temperature and/or density? 

- QCD predicts QGP

- Consensus: Energy density big enough

- Consensus:  Matter strongly interacts with itself; should be thermalized

## We want to measure:

- Sound speed

- Number of degrees of freedom?
- Change in energy density from hadron gas to quark gluon plasma?

- Properties of resonances in media and relationship to:
- Confinement and mass generation?
- Screening length?

- Temperature?

- Partially resolved puzzle of comparing measured lifetimes and sizes from computation with measurement.
- Mass generation?

- Baryon number excess at moderate pT?

## Is this relevant for naturally occurring phenomena?

- Some gamma ray bursters sit around for days to years after supernova explosions before going hypernova.
- Black hole formation?  Metastable QGP?
- Many RHIC theorists also think about such things!
- Hydro tools, theory of high energy density matter
- The QGP began in the theory of high baryon density matter!

- Matter at very high baryon density and low T:

- T small, density ~ 10-20 baryons/fm

- 3

## What is the nature of gluonic matter? 

- How does this matter appear in strongly interacting particles?

- Glue binds all quarks inside of hadrons.
- It is 1⁄2 of the momentum of a high energy proton.
- It is responsible for confinement and mass generation.
- By an order of magnitude, the soft degrees of freedom of a high energy strongly interacting particle is glue.

- We understand very little about this gluonic matter!

- HERA

## Where do the gluons go?

- Cross sections grow slowly.

- Gluon density grows very rapidly.

- QCD coupling becomes weak, but interactions are strong because of coherence

- Heavy ions at high energies are a gluon wall

## What is the Color Glass Condensate?

- Glue at large x generates glue at small x
- Glue at small x is classical field
- Time dilation -> Classical field is glassy
- High phase space density -> Condensate

- Phase space density:

- Attractive potential

- Repulsive interactions

- Phase Space Density

- is small

- is big

## Why is the Color Glass Condensate Important?

- It is a new universal form of matter:
- Matter:  Carries energy; Separation of gluons is small compared to size of system; Number of gluons is large

- New:  Can only be made and probed in high energy collisions

- Universal:  Independent of hadron, renormalization group equations have a universal solution.
- Universality <=> Fundamental

- It is a theory of:
- Origin of glue and sea quarks in hadrons
- Cross sections
- Initial conditions for formation of Quark Gluon Plasma in heavy ion collisions

_**Nuclei provide highest density and largest sizes => Simplicity**_

## CGC predicted particle production at RHIC

- Proportionality constant can be computed.

## 16

- Data from dA collisions at RHIC Consistent with CGC

- Look for fragments of deuteron since they measure them smallest x properties of the nucleus

- Back to back jet correlations seen in STAR?

- Detailed studies of x dependence?

## How are spin and baryon number distributed inside of nucleons?

- Spin and baryon number carry the valence quantum numbers of hadrons
- They involve collective excitations of the glue with quark degrees of freedom and/or topological excitations
- They typically generate **much **more transfer of valence quantum numbers to the soft (small x or wee) degrees of freedom than one had naively expected.
- They are of immense theoretical interest, and there is considerable controversy in understanding their properties
- Little is known about the distribution of spin from experiment.

## Quark Gluon Plasma and Color Glass Condensate at RHIC, LHC and eRHIC

_**RHIC:**_
_**RHIC HAS DEMONSTRATED IT CAN PRODUCE AND STUDY QGP **_
_**SPIN PROGRAM IS UNIQUE**_
- QGP measurements involve much study of correlated phenomena sometimes in different environments =>
_**TIME AND LUMINOSITY IMPORTANT**_
- Has and will measure many properties of CGC before LHC has dA or pA
_**BEING FIRST IS ALWAYS GOOD**_

_**LHC:**_
- QGP study is harder because CGC strongly modifies gluon distributions in nuclei relative to proton.
- Can probe very small x and very large momenta
- Need dA or pA, and time.

_**eRHIC:**_
- Study of spin and CGC becomes a precision science.
- Electron probes much less sensitive to final state physics

## Lattice Gauge Theory

- Tests QCD

- Tests Confinement

- Computes Masses

- Compute Finite T QCD

-       QCDOC Project at BNL promises
- 10+ TFlops (x 2)
- allowing for computations
- with realistic quark masses
- RBRC

## Summary:

- RHIC has fundamentally changed our knowledge of strong interactions.
- RHIC has made a sQGP
- RHIC has probably seen the CGC

## What are the theoretical and computing needs of RHIC science and are they available?

- Young people want to work on RHIC theory.
- Resources for students and postdocs are very tight.
- Many group may have to eliminate postdocs and students.
- We have successfully placed young people from this field in faculty positions.
- RBRC is under stress if spin program at RHIC is weakened.
- Young people are our present and our future!

- Computing for lattice gauge theory has new machines.
- Effort for simulation of RHIC collisions needs computing and people resources

- Potential meltdown of lab and university theory efforts:
- Resources are people intensive.
- RBRC

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