Gluon recombination in high parton density QCD: inclusive $\pi$-meson production

We argue that the collinear factorization of the fragmentation functions in high energy hadron and nuclei collisions breaks down at transverse momenta $k_T \alt Q_s/g$ due to high parton densities in the colliding hadrons and/or nuclei. We calculate, at next-to-leading order in projectile parton density and to all orders in target parton density, the double-inclusive cross section for production of a pair of gluons in the scalar $J=0^{++}$ channel. Using the low energy theorems of QCD we find the inclusive cross section for $\pi$-mesons production.