Parton transverse momenta and direct photon production in hadronic collisions at high energies (original) (raw)

The invariant cross sections for direct photon production in hadron-hadron collisions are calculated for several initial energies (SPS, ISR, SppS, RHIC, Tevatron, LHC) including initial parton transverse momenta within the formalism of unintegrated parton distributions (UPDF). Different approaches from the literature are compared and discussed. A special emphasis is put on the Kimber-Martin-Ryskin (KMR) distributions and their extension into the soft region. Sum rules for UPDFs are formulated and discussed in detail. We find a violation of naive number sum rules for the KMR UPDFs. An interesting interplay of perturbative (large k{sub t}²) and nonperturbative (small k{sub t}²) regions of UPDFs in the production of both soft and hard photons is identified. The k{sub t}-factorization approach with the KMR UPDFs is inconsistent with the collinear approach at large transverse momenta of photons. Kwiecinski UPDFs provide very good description of all world data, especially at super proto...