Clarify higher-order corrections for prompt-photon production

Clarify the impact of NNLO QCD corrections on the absolute ATLAS prompt-photon spectra in proton-lead collisions before including these measurements in the nCTEQ nuclear PDF analysis.

Background

Prompt-photon production provides a relatively clean probe of the nuclear gluon distribution. The ATLAS proton-lead absolute spectra, however, are poorly described by current calculations, despite ratios being broadly compatible with previous nuclear-modification determinations.

The discrepancy may arise partly from missing higher-order effects. The authors consequently postpone inclusion of the ATLAS data until the role of NNLO corrections is understood.

References

As for the dijet data, missing higher order effects might be part of the explanation. As a consequence, we do not yet include the ATLAS prompt photon data in our global analysis, until the impact of NNLO corrections {Campbell:2016lzl,Chen:2022gpk} has been clarified.

— nCTEQ26 nuclear parton distribution functions  (2610.13633 - Collaboration et al., 9 Oct 2026) in Section 10.3, subsection “ATLAS/ALICE prompt photons”