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

Abstract

We compare the results of the 2 → 1 kt-factorization approach (often called BFKL multi-Regge factorization) with Kwieciński unintegrated parton distribution functions (UPDF) 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 kt-factorization approach also includes 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 kt-factorization approach gives a much better description of the pt∼ 1–4 GeV region than the leading order collinear approach both at mid- and forward-rapidity regions. Our approach leads to asymmetry in the production of π+ and π−, very similar to that observed very recently by the BRAHMS Collaboration.