Unintegrated parton distributions and pion production in proton-proton collisions at high energies

Abstract

Inclusive cross sections for pion production in proton-proton collisions are calculated for the first time based on unintegrated parton (gluon, quark, antiquark) distributions (uPDF). We use Kwieci\'nski uPDF's and phenomenological fragmentation functions from the literature. In addition to the $gg \to g$ diagram used recently for applications at RHIC we include also $g q \to q$ and $q g \to q$ diagrams. We find that the new contributions are comparable to the purely gluonic one at midrapidities and dominate in the fragmentation region. The new mechanisms are responsible for $\pi^+ - \pi^-$ asymmetry. We discuss how the asymmetry depends on $x_F$ and $p_t$. Inclusive distributions in $x_F$ (or rapidity) and transverse momentum for partons and pions are shown for illustration. In contrast to standard collinear approach in our approach the range of applicability can be extended towards much lower transverse momenta.