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 Kwieciński uPDF's and phenomenological fragmentation functions from the literature. In addition to the gg → g diagram used recently for applications at RHIC we include also gq → q and qg → 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 π + − π − 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.

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

“…While at large (pseudo)rapidities (η = 2.2, 3.2) our results (negative pions) are quite compatible with the experimental result for negative hadrons, there seems to be a missing A, B 1 and B 2 in Fig.1 of Ref. [13]. While at η = 0 the gg → g contribution dominates up to p t ∼ 3.5 GeV at η = 2.2 the B 1 contribution is larger than the gg → g one already at p t ∼ 1.5 GeV and at η = 3.2 above p t ∼ 1 GeV.…”

“…The k tfactorization is much better but still some contribution is missing at large Feynman x F and at small transverse momenta. However, one should remember that other processes such as In Fig.4 we show our full result (diagrams A, B 1 and B 2 [13]) for different fragmentation functions [23,24,26]. In this calculation b 0 = 0.5 GeV −1 was used.…”

“…In Ref. [13] we have included two other leading-order diagrams which involve quark degrees of freedom. They are important in the so-called fragmentation region [13].…”

“…We have applied these unintegrated parton distributions to gauge boson [19], standard Higgs [20] hadroproduction as well as for charm-anticharm photoproduction [21]. Very recently we have applied this formalism also to the description of the SPS pion production data [13].…”

“…Recently we have supplemented the mechanisms including the gluon degrees of freedom with mechanisms including the quark degrees of freedom [13]. The latter are very important at very forward (η ≫ 0) and very backward (η ≪ 0) rapidity regions.…”