5.3 Gluon Saturation and the Formation Stage of Heavy Ion Collisions Primordial Bulk Plasma Dynamics in Nuclear Collisions at RHIC

Gluons are ultimately responsible for greatest part of the mass of visible matter in the universe. The gluonic contribution to mass has its origin in the gluonic cloud which surronds light mass quarks. This cloud results in about 99% of the mass of a proton or neutron. Gluons generate the strong force. This force permanently confines quarks and gluons inside of nucleons. The nucleon-nucleon force, responsible for making atomic nuclei, has its origins in gluons. We know very little of gluons by direct experiment. Their existence is inferred indirectly. Approximately 1/2 of the momentum of a fast moving proton is in gluons. This is known because the contribution of directly measured quarks only gives one half of the total momentum of the proton. By measuring the distributions of quarks inside a proton and their variation with the momentum scale of the measuring probe, one can extract the implied distribution of gluons. By measurement of the production of high transverse momentum jets of particles produced in collisions of strongly interacting particles, one can measure gluon distributions, but with strong restrictions that the momentum scale of the jets is large, and with uncertainties associated with jet hadronization.