Soft-gluon resummation and NNLO corrections for direct photon production
Nikolaos Kidonakis, J. F. Owens
TL;DR
This work develops soft-gluon threshold resummation for direct photon production in hadronic collisions, deriving a resummed cross section and expanding it to NNLO to capture NNLL terms. The authors validate the approach by matching to exact NLO results and show that NNLO corrections significantly reduce scale dependence, though they do not fully resolve discrepancies with fixed-target data. The numerical studies, using existing NLO-type codes augmented with NNLO-like terms, indicate improved perturbative stability but highlight remaining tensions with E-706/UA-6 measurements and the need for further refinement and experimental input. Overall, the paper provides a concrete, higher-precision framework for direct photon production near threshold and establishes a basis for future theoretical and phenomenological improvements.
Abstract
The resummation of threshold logarithms for direct photon production cross sections in hadronic collisions is presented. The resummation is based on the factorization properties of the cross section and is formulated at next-to-leading logarithmic or higher accuracy. Full analytical and numerical results for the next-to-next-to-leading order expansion of the resummed cross section are given. A substantial reduction of factorization scale dependence is observed. A comparison to experimental results from the E-706 and UA-6 experiments is presented.