High Energy Collisions of Dense Hadrons in Quantum Chromodynamics : LHC Phenomenology and Universality of Parton Distributions

摘要

As the value of the longitudinal momentum carried by partons in aultra-relativistic hadron becomes small, one observes a growth of theirdensity. When the parton density becomes close to a value of order$1/\alpha_s$, it does not grow any longer, it saturates. These high densityeffects seem to be well described by the Color Glass Condensate effective fieldtheory. On the experimental side, the LHC provides the best tool ever forreaching the saturated phase of hadronic matter. For this reason saturationphysics is a very active branch of QCD during these past and coming years sincesaturation theories and experimental data can be compared. I first deal withthe phenomenology of the proton-lead collisions performed in winter 2013 at theLHC and whose data are about to be available. I compute the di-gluon productioncross-section which provides the simplest observable for finding quantitativeevidences of saturation in the kinematic range of the LHC. I also discuss thelimit of the strongly correlated final state at large transverse momenta and bythe way, generalize parton distribution to dense regime. The second main topicis the quantum evolution of the quark and gluon spectra in nucleus-nucleuscollisions having in mind the proof of its universal character. This result isalready known for gluons and here I detail the calculation carefully. Forquarks universality has not been proved yet but I derive an intermediateleading order to next-to leading order recursion relation which is a crucialstep for extracting the quantum evolution. Finally I briefly present anindependent work in group theory. I detail a method I used for computing tracesinvolving an arbitrary number of group generators, a situation oftenencountered in QCD calculations.