Measurement of the Production Cross Section of Pairs of Isolated Photons   with CMS
  In this paper we present the measurement of the integrated and differential production cross sections of pairs of prompt isolated photons in proton-proton collisions at a centre-of-mass energy of 7 TeV with the Compact Muon Sollenoid (CMS) detector at the Large Hadron Collider (LHC). A next-to-leading order (NLO) perturbative QCD (pQCD) prediction was compared to the measurement, which was performed on a sample corresponding to an integrated luminosity of 36 inverse picobarn. While the agreement on integrated cross sections is satisfactory, a discrepancy is observed in the region of the phase space populated by photons with small relative angle, where the theoretical prediction underestimates the measured cross section. 
Laurent Millischer
hep-ex