2006/06/29 by T. Pietrycki, Antoni Szczurek, A. Szczurek · 2 citations
Physics and Astronomy · #High-Energy Particle Collisions Research #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions #hep-ph
paper · pdf · doi:10.1103/physrevd.75.014023
published as Phys.Rev.D75:014023,2007 · 19 pages, 23 figures
arxiv created 2006/06/29 · openalex publication_date 2007/01/25 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
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 kt2) and nonperturbative (small kt2) regions of UPDFs in the production of both soft and hard photons is identified. The kt-factorization approach with the KMR UPDFs is inconsistent with the collinear approach at large transverse momenta of photons. Kwieci\ifmmode \acuten\else 'n\fiski UPDFs provide very good description of all world data, especially at super proton synchrotron (SPS) and intersecting storage rings (ISR) energies. Off-shell effects are discussed and quantified. Predictions for the CERN LHC are given. Very forward/backward regions in rapidity at LHC energy are discussed and a possibility to test unintegrated gluon distributions (UGDF) is presented.