Nuclear size and rapidity dependence of the saturation scale from QCD evolution and experimental data
J. L. Albacete, N. Armesto, J. G. Milhano, C. A. Salgado, U. A. Wiedemann
TL;DR
The paper addresses how the QCD saturation scale depends on rapidity and nuclear size by solving the Balitsky–Kovchegov evolution equation for various coupling scenarios. It compares fixed- and running-coupling evolutions using different kernel prescriptions (K1–K3) and initial conditions (GBW, MV, AS), linking the evolution of the dipole amplitude to the observed geometric-scaling patterns in lepton-nucleus and nucleus-nucleus data. Key findings show that fixed coupling drives faster evolution, while running coupling slows the approach to saturation, with only small differences among kernel choices; the high-k tail is influenced by the chosen initial condition. The work connects theoretical BK evolution to experimental scaling, informing the rapidity and size dependence of saturation in high-energy hadronic and nuclear collisions.
Abstract
The solutions of the Balitsky-Kovchegov evolution equations are studied numerically and compared with known analytical estimations. The rapidity and nuclear size dependences of the saturation scale are obtained for the cases of fixed and running coupling constant. These same dependences are studied in experimental data, on lepton-nucleus, deuteron-nucleus and nucleus-nucleus collisions, through geometric scaling and compared with the theoretical calculations.