Aspects of QCD at high energies and their Phenomenological Consequences
We study the high-energy limit of QCD using the DGLAP, BFKL and B-JIMWLK frameworksbased on non-standard perturbative re-summation techniques to calculate the theory predictionsfor the cross section of semi-hard processes in these little explored kinematic domains.In particular, we have studied forward-backward dijet production initiated by hadronic or pho-tonic scattering, which is characterized by two alternative signatures: “jet-gap-jet” events, with theformation of a rapidity gap between the jets, or, inclusive dijets, with any radiation in the rapidityregion in between. To this end, we have, on the one hand, calculated new theoretical predictions us-ing the BFKL framework and, on the other hand, we have investigated these and other predictionsin dedicated phenomenological analyses (1; 2).We found that the BFKL factorization property of “jet-gap-jet” cross sections is violated athigher precision, requiring a rethinking of the physical picture currently used to describe this pro-cess. Nevertheless, we have shown that the violation is small at current energies. We have alsogiven a tentative explanation for the origin of the violation, and we have indicated a promising wayto reformulate the factorization properties of these processes.We have also proposed a new model (3) that takes into account the impact parameter distributionof the initial state nuclear structure — the transverse projection of nuclear matter centered at thecollision point — in shaping the forward-forward dijet distribution in dilute-dense regimes. Dilutefast moving partons are used to probe the small longitudinal momentum tail of the nuclear partonicdistribution, whose transverse motion can no longer be neglected and requires a description interms of transverse momentum distribution functions. At the same time, the large density of slow-moving partons in the nuclear cloud should be sensitive to gluon saturation effects, as dictated bythe B-JIMWLK evolution equations. We show that the process signature is rather sensitive to thesaturation model employed, suggesting that an inclusive description in the impact parameter spacefails to capture important contributions to the physics of saturation.
Networked Digital Library of Theses and Dissertations