Diffractive Excitation in DIS and pp Collisions

TL;DR

The paper extends Mueller's dipole cascade to include confinement effects via a screened Yukawa potential and energy-momentum conservation, achieving improved frame independence and a more complete treatment of fluctuations. It employs an eikonal/Good–Walker framework to study elastic and diffractive scattering, accounting for fluctuations from the cascade evolution, dipole–dipole interactions, impact parameter dependence, and the initial photon and proton wavefunctions. The approach yields good agreement with Tevatron and HERA data and provides predictions for the LHC, with the confinement model controlling large-dipole contributions and two main parameters, $r_{ ext{max}}$ and $\Lambda_{ ext{QCD}}$, governing normalization and energy dependence. This work enhances the understanding of diffractive processes in high-energy $pp$ and DIS and offers a more robust, frame-independent description of nonperturbative effects in high-energy QCD.

Abstract

We have in earlier papers presented an extension of Mueller's dipole cascade model, which includes subleading effects from energy conservation and running coupling as well as colour suppressed effects from pomeron loops via a ``dipole swing''. The model was applied to describe the total cross sections in pp and gamma*p collisions. In this paper we present a number of improvements of the model, in particular related to the confinement mechanism. A consistent treatment of dipole evolution and dipole--dipole interactions is achieved by replacing the infinite range Coulomb potential by a screened potential, which further improves the frame-independence of the model. We then apply the model to elastic scattering and diffractive excitation, where we specifically study the effects of different sources for fluctuations. In our formalism we can take into account contributions from all different sources, from the dipole cascade evolution, the dipole--dipole scattering, from the impact-parameter dependence, and from the initial photon and proton wavefunctions. Good agreement is obtained with data from the Tevatron and from HERA, and we also present some predictions for the LHC.