On Angular Correlations and High Energy Evolution
Alex Kovner, Michael Lublinsky
TL;DR
The paper investigates whether JIMWLK evolution can capture angular correlations in high-energy hadronic wave functions. It uses a projectile dipole model with anisotropic initial conditions and BK evolution to study how these angular correlations evolve, and finds that correlations decay exponentially with rapidity, even inside the saturation radius. The results indicate that JIMWLK alone misses important short-range correlations and that Pomeron loop effects are necessary to preserve angular structure, especially for modes around the saturation scale Q_s. Consequently, accurately predicting high-energy angular correlations requires combining KLWMIJ and JIMWLK evolutions and incorporating Pomeron-loop dynamics, with implications for interpreting ridge-like phenomena in high-multiplicity hadron collisions.
Abstract
We address the question to what extent JIMWLK evolution is capable of taking into account angular correlations in a high energy hadronic wave function. Our conclusion is that angular (and indeed other) correlations in the wave function cannot be reliably calculated without taking into account Pomeron loops in the evolution. As an example we study numerically the energy evolution of angular correlations between dipole scattering amplitudes in the framework of the large $N_c$ approximation to JIMWLK evolution (the "`projectile dipole model"'). Target correlations are introduced via averaging over (isotropic) ensemble of anisotropic initial conditions. We find that correlations disappear very quickly with rapidity even inside the saturation radius. This is in accordance with our physical picture of JIMWLK evolution. The actual correlations inside the saturation radius in the target QCD wave function, on the other hand should remain sizable at any rapidity.