Multi-particle production in the Color Glass Condensate

Abstract

In this thesis, we review the framework of multi-particle production in high energy collisions within the Color Glass Condensate effective theory. The main goal of this work is to provide a systematic basis for performing analysis on particle correlation both in proton-proton, pp, and in proton-nucleus, pA, scatterings such as those studied at the LHC or RHIC. We provide the basic aspects of the high energy, or small-x, limit of Quantum Chromodynamics (QCD) and we introduce the Color Glass Condensate (CGC). We provide the technical approach for studying particle production in high energy collisions at leading order in the QCD coupling constant. We review the phenomenon of particle correlation that has been seen in pp and pA collisions and we explain it from first principles within the CGC framework. On the other hand, based on [38], we generalize the usual approach for analyzing particle production at leading order within the CGC framework to the case in which an arbitrary number of particles are produced. We introduce and study the so-called Area Enhancement model which offers a simple alternative for evaluating high order Wilson lines correlators. We mimic the Gaussian ansatz of the Wigner distribution approach for studying multi-particle correlations but we break the usual factorization assumption. We compute the 4-particle cumulant, c2{4}, and we obtain a negative value which agrees qualitatively with data. Finally, based on [45,46], we introduce sub-eikonal corrections to the dilute-dilute, or Glasma Graph, limit of the CGC by including finite width effects. We study the effects of non-eikonal corrections in single, double and triple gluon production. We see that the sub-eikonal effects introduces an asymmetry in the azimuthal distribution of gluons and therefore is able to explain the appearance of odd azimuthal harmonics in data. We perform a numerical study of the non-eikonal effects and see that they are negligible at relatively high energies. We generalize our approach to the dilute-dense limit, which is more suitable for pA collisions, by introducing the dense medium propagator, analogously to the jet quenching framework. We introduce a systematic approach for computing multigluon production in proton-nucleus collisions beyond the eikonal accuracy. We study the odd azimuthal harmonics generated in this approach.