DIRECT PHOTON PRODUCTION IN pp AND $p {\bar p}$ COLLISIONS AT HIGH ENERGIES

Abstract

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). Kwieciński UPDFs provide very good description of all world data, especially at SPS and ISR energies. Inclusion of the QCD evolution effects and especially their effect on initial parton transverse momenta allowed to solve the longstanding problem of understanding the low energy and low transverse momentum data.

Measurement of Direct Photons in pp and Pb–Pb Collisions with ALICE

“…In pp collisions, leading order pQCD processes, quark-gluon compton-scattering and quark-anti-quark annihilation are the main components of direct-photon production at high p T . The second source is photons produced in yet fragmentation [1]. In heavy-ion collisions these prompt photons should be enhanced by the larger number of binary collisions.…”

“…The comparison to pp pQCD results at higher p T tests the binary scaling behavior of initial hard scatterings. 1 A list of members of the ALICE Collaboration and acknowledgements can be found at the end of this issue.…”