The CGC and the Glasma: Two Lectures at the Yukawa Institute
2010
These lectures present the theory of the
Color Glass Condensate(CGC) and the Glasma in an elementary and intuitive manner. This matter controls the high energy limit of QCD. The CGC is the universal limit for the components of a
hadronwavefunction important for high energy scattering processes. It is a highly coherent, extremely high energy density ensemble of
gluonstates. The Glasma is matter produced in the collision of CGCs of two
hadrons. It has properties much different from those of the CGC, and is produced in a very short time after the collision. It eventually evolves from the the
Color Glass Condensateinitial conditions into a
Quark Gluon Plasma. We can visualize the collision of two high energy
hadronsas shown in Fig. 1. Before the collision, two
hadronsappear as Lorentz contracted sheets approaching one another at near light speed. These we will later describe as two sheets of Colored Glass. In a very short time, the sheets of Color Glass interpenetrate one another. This we think of as the
initial singularityfor the collision. This is of course not a real singularity for finite collision energy, but we will see it becomes one in the limit of infinite energy. After the
initial singularity, a Glasma is formed. This is composed of highly coherent
gluon fieldsof very high energy density. If we imagine that the sheets of Colored Glass have passed through one another largely intact, the Glasma forms in the region between the receding sheets. As time goes on, the Glasma evolves into a
Quark Gluon Plasma, and eventually into a gas of ordinary
hadrons. These lectures are about the earliest stages of these collisions, and will describe neither the
Quark Gluon Plasmanor the
HadronGas. I will motivate the CGC and Glasma from simple physical considerations, and provide a sketchy derivation from QCD. There will be some discussion of experimental tests of these ideas.
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