Factorization, the Glasma and the Ridge in heavy ion collisions

High energy heavy ion collisions can be efficiently described as the collision of two sheets of Color Glass Condensate. The dynamics of the collision can be studied ab initio in a systematic effective field theory approach. This requires factorization theorems that separate the initial state evolution of the wave functions with energy from the final state interactions that produce matter with high energy densities called the Glasma. We discuss how this matter is formed, its remarkable properties and its relevance for understanding thermalization of the Quark Gluon Plasma in heavy ion collisions. Long range rapidity correlations in the collision that have a remarkable ridge like structure may allow us to probe early times in the collision and infer directly the properties of the Glasma.