Measurement of the Production Cross Section for Pairs of Isolated   Photons in pp collisions at sqrt(s) = 7 TeV
  The integrated and differential cross sections for the production of pairs of isolated photons is measured in proton-proton collisions at a centre-of-mass energy of 7 TeV with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 36 inverse picobarns is analysed. A next-to-leading-order perturbative QCD calculation is compared to the measurements. A discrepancy is observed for regions of the phase space where the two photons have an azimuthal angle difference, Delta(phi), less than approximately 2.8. 
CMS Collaboration
hep-ex