Unintegrated gluon distribution from modified BK equation

Abstract

We investigate the recently proposed nonlinear equation for the unintegrated gluon distribution function which includes the subleading effects at small $x$. We obtained numerically the solution to this equation in $(x,k)$ space, and also the integrated gluon density. The subleading effects affect strongly the normalization and the $x$ and $k$ dependence of the gluon distribution. We show that the saturation scale $Q_s(x)$, which is obtained from this model, is consistent with the one used in the saturation model by Golec-Biernat and W\"usthoff. We also estimate the nonlinear effects by looking at the relative normalization of the solutions to the linear and nonlinear equations. It turns out that the differences are quite large even in the nominally dilute regime, that is when $Q^2 \gg Q_s^2$. Finally, we calculate the dipole-nucleon cross section.