QCD in the Regge-Gribov limit: an introduction to the Color Glass Condensate (CGC) EFT
ABSTRACT :
One of the crucial observations from the electron-proton DIS data at HERA is the predominance of gluons in the hadronic wavefunction and the burgeoning of gluon densities at high energies or small Bjorken-x. It is conjectured that repulsive gluon recombination and screening effects rival against bremsstrahlung to attenuate this resulting growth of high energy cross-sections, in conformity with constraints imposed by unitarity. As an outcome of these competing effects, a semi-hard saturation scale, Q_{s}(x) dynamically emerges which allows the use of effective field theory techniques to systematically compute the otherwise non-linear, many-body gluodynamics of this novel regime of QCD. This physical intuition is concretized in a Wilsonian renormalization group (RG) framework known as the Color Glass Condensate (CGC) effective field theory (EFT).
In this talk, I will discuss the basics of this formalism that describes the initial state of nucleonic matter in heavy ion collisions. Starting with the classical version originally theorized for an infinite nucleus I will discuss the generalization for realistic nuclei. This will be followed by the computational tools that reflect the power of the CGC EFT to extend ab-initio techniques for phenomenological analyses of collision data. In the last part of this talk, I will show the application of these theoretical tools towards a first computation of the differential cross-section for inclusive photon+dijet production at small x.