The Color Glass Condensate: Theory, Experiment and the Future

Transcription

1 The Color Glass Condensate: Theory, Experiment and the Future Physics Issues: What is the high energy limit of strong interac?ons? How do we compute the gluon and quark distribu?ons relevant for asympto?cally high energy interac?ons? What are the possible states of high energy density mager? Is there a simple unified descrip?on of lepton- hadron and hadron- hadron interac?ons? Where? Deep inelas?c scagering and diffrac?on at Heavy ion collisions and da collisions at RHIC energies and above LHC

2 The gluon density is high in the high energy limit: Gluons dominate the proton wavefunc?on Evolu?on at fixed resolu?on scale is towards high density But proton size grows slowly Evolu?on at fixed x is towards dilute distribu?on of large numbers of partons Gribov, Levin and Ryskin; Mueller, Qiu

3 Mclerran and Venugopalan At high gluon density the coupling is weak, so should be able to compute the proper?es of this high gluonic density state using weak coupling methods within QCD Imagine gluon as a sphere of size act like a hard sphere At fixed resolu?on scale pact un?l the phase space density The Bjorken- Feynman parton model of incoherent quark and gluon distribu?ons is generalized to classical gluon fields Once the phase space density is saturated, then begin to fill up hadron with smaller size gluons High phase space density => Classical Limit Color: Gluons are colored Condensate: The phase space density of gluons is high and is self- generated Glass: The classical field corresponding to slow moving partons arises from fast moving partons and therefore evolves on?me scales long compared to natural ones: Distribu?on is incoherent distribu?on of sources like spin glasses

4 Theore?cal Developments: Well developed and intui?ve formalism for compu?ng deep inelas?c scagering and diffrac?on. Good and simple descrip?on of data. JIMWLK Evolu?on equa?ons to all orders in the background fields that for correla?on func?ons is Balitsky- Kovcehgov hierarchy. NLO computa?ons performed. Evolu?on equa?ons predict universal solu?on at small x Is it weakly coupled? How coherent? Color Glass Condensate: Theory of source of color charge Source produces stochas?c distribu?on Of non- abelian Lorentz boosted Coulomb fields. Gluonic operators are expressed in terms of classical field and averaged over incoherent distribu?on of sources McLerran- Venugopalan model is Gaussian distribu?on of sources

5 Experimental Evidence: ep Collisions Computed satura?on momentum dependence on x agrees with data Simple explana?on of generic feature of data Allows an extrac?on of satura?on momentum

6 Experimental Evidence: ep Collisions Diffrac?on

7 But there exist other non- satura?on interpreta?ons. Are there really no or even a nega?ve number of valence gluons in the proton for small x?

8 High Energy Collisions: Explicit realiza?on of Bjorken space-?me picture Instantaneously develop longitudinal color E and B fields! Two sheets of colored glass collide! Glass melts into gluons and thermalize! QGP is made which expands into a mixed phase of QGP and hadrons!

9 The Glasma and CGC allow a theore?cally consistent predic?on of: Ini?al gluon mul?plicity and transverse momentum distribu?ons Shadowing and dependence on par?cipant number in heavy ion collisions Heavy quark dependence upon par?cipant number in heavy ion collisions Fluctua?ons in the mul?plicity distribu?on Long range rapidity correla?ons Two par?cle correla?ons Provides a framework for addressing issues such as: Thermaliza?on Topological charge fluctua?ons and even by event viola?ons of P and CP First principles deriva?on e.g.: Factoriza?on theorems that generalize those of perturba?ve QCD into the saturated region

10 Jet Quenching in da Collisions: Forward backward angular correla?on between forward produced, and forward- central produced par?cles 200 GeV p+p and d + Au Collisions Run8, STAR Preliminary pp d+au (peripheral) d+au (central)

11 Satura?on and the LHC Ignoring slow varia?on of coupling constant and total cross sec?on with energy from HERA, take

12 Geometric Scaling of transverse momentum distribu?ons

13 Mul?plicity Fluctua?ons and Transverse Momentum

14 The EIC Data for RHIC indicate that for a number of effects that can be ascribed to satura?on are rapidly turning on for large nuclei Would like precise tests of the CGC hypothesis. Is the theory capable of precise computa?ons for such values of the satura?on momentum? Is it possible to get precise results for nuclei on interes?ng quan??es such as the longitudinal structure func?on?