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

Wavefunction has: 3 quarks 3 quarks plus 1 gluon 3 quarks plus 2 gluon ……. 3 quarks plus many gluons The Gluon Wall: 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 potentialRepulsive interactions Density as high as it can be Because the density is highis 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 sheetis 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?

What are the Quasi Particles of the Glass? 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. 17

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 ……..