# Presentation: 505519

## The Color Glass Condensate

- Outstanding questions:

- What is the high energy limit of QCD?

- How do gluons and quarks arise in hadrons?

- What are the possible forms of high density matter?

- Claim:  CGC is a universal form of strongly interacting matter which controls the high energy limit of QCD, and form which the gluons and quarks arise in this limit.

- 1

## 2

- How do we think about a high energy hadron?

- Work in fast moving frame:

- High Energy Limit is Small x Limit

## The Gluon Wall:

- Wavefunction has:
- 3 quarks
- 3 quarks plus 1 gluon
- 3 quarks plus 2 gluon
- .......
- 3 quarks plus many gluons

- Important matrix elements at high energies have lots of gluons in them

- 3

## 4

- In RHIC Collisions
- Au-Au at 100GeV/Nucleon in each beam
- About 1000 slow moving (small x) particles are
- made in central collisions

## Where do all the gluons go?

- Cross sections for hadrons rise very slowly with energy

- But the gluon density rises much more rapidly!
- The high energy limit is the high gluon density limit.
- Surely the density must saturate for fixed sizes of gluons at high energy.

- 5

## 6

- 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

- Density as high as it can be

- Because the density is high

- is small

- is big

## 7

- There must be a renormalization group

- The x which separates high x sources from small x fields is arbitrary

- Phobos multiplicity data

- High energy QCD “phase” diagram

## 8

- 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 collsions

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

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

## 9

- What does a sheet of Colored Glass look like?

- On the sheet

- is small

- Independent of

- big

- small

- Density of gluons per unit area

- Lienard-Wiechart potentials
- Random Color

## 10

- The Color Glass Condensate Explains Growth of Gluons at Small x

- Renormalization group equation predicts:

- Gluon pile up at fixed size until

- gluons with strength

- act like a hard sphere

- Once one size scale is filled
- Move to smaller size scale
- Typical momentum scale grows

## 11

- The CGC Explains Slow Growth of Total Cross Section

- Transverse distribution of gluons:

- Transverse profile set by initial conditions

- Size is determined when probe sees a fixed number of particles at some transverse distance

## 12

- CGC Explains Qualitative Features of Electron-Hadron Scattering

- Function only of a particular combination of Q and x
- Scaling relation

- Works for

- Can successfully describe quark and gluon distributions at small x and wide range of Q

- Q is resolution momentum of photon, x is that of struck quark

## 13

- CGC Gives Initial Conditions for QGP in Heavy Ion Collisions

- Two sheets of colored glass collide
- Glass melts into gluons and thermalize
- QGP is made which expands into a mixed phase of QGPand hadrons

- Mystery:  The QGP is very strongly interacting:
- Arnold and Moore suggest heating may be due to instabilities in melting CGC

## 14

- CGC predicted particle production at RHIC

- Proportionality constant can be computed.

## 15

- CGC provides a theory of shadowing (modification of quark and gluon distributions in nuclei)

- Two effects:
- Multiple scattering:  more particles at high pT
- CGC modification of evolution equations => less particles

## 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?

## 17

- Regge (with Gorbachov)

- Pomerons:  Two gluon C even state
- Reggeons: Multiple gluon, multiple quark states
- Odderon:  C odd three gluon state; Pomeron gives imaginary part of T matrix and odderon  real part at high energy

- Quasi-particles are excellent probes of properties of a media.

- Quasi particles of the glass are pomeron, odderon, reggeon etc.
- Were inferred long ago from scattering matrix theory.
- Computable small fluctuation of color glass

- Can be probed in pp, pA and eA interactions.
- Polarized scattering a good probe.

## 18

- Exciting times for theory:

- Beginning of a complete description  of high energy limit of QCD
- Must understand the collective excitations of the CGC: pomerons, reggeons, odderons...
- Need to understand interactions of these collective excitations: ploops or Pomeron loops
- Relationships with universal behavior of nucleation models.
- Solitons
-         More........