Two opposite-side large-pTphotons in perturbative QCD

Abstract
Production of two opposite-side large-pT photons in hadronic collisions is studied in perturbative QCD. Apart from the Born process qq¯→γγ, contributions from gg→γγ (box graph) and qg→qγγ (bremsstrahlung) are calculated. Higher-order corrections (K factors) to all these contributions are taken into account, leading to approximate upper and lower bounds on the theoretical predictions. Recent data, in particular from proton-nucleon collisions, clearly exceed the predictions.