Unintegrated parton distributions and pion production in pp collisions at RHIC's energies

Abstract

We compare results of $2 \to 1$ $k_t$-factorization approach with Kwieci\'nski unintegrated parton distributions and the standard collinear factorization approach at RHIC and slightly smaller energies. Our approach contains only one free parameter responsible for internal parton motion in nucleons. In contrast to recent works in the literature our $k_t$-factorization approach includes also quark degrees of freedom in addition to purely gluonic terms. Both mid and forward rapidity regions are considered. We discuss uncertainties due to fragmentation functions. In general, the $k_t$-factorization approach gives a better description of the $p_t \sim$ 1 -- 4 GeV region both at mid and forward rapidity regions. Our approach leads to asymmetry in the production of $\pi^+$ and $\pi^-$, very similar to the one observed very recently by the BRAHMS collaboration.