Measurement of the differential isolated diphoton production cross section in pp collisions at sqrt(s) = 7 TeV with the CMS detector

The measurement of the isolated diphoton production cross section in pp collisions at $\sqrt{s}$~=~7~\TeV is presented. The dataset corresponds to an integrated luminosity of 5.0~fb$^{-1}$ collected by the CMS experiment in the year 2011. A new data-driven method to extract the prompt diphoton yield is used, based on the photon component of the particle-flow isolation. The measured cross section for two isolated photons with transverse momentum above 40 GeV and 25 GeV respectively, in the acceptance $|\eta| < 2.5, |\eta| \notin [1.44,1.57]$ and with an angular separation $\Delta R > 0.45$, is $(16.8\pm 1.8)$ pb. The cross section is measured differentially as a function of the diphoton invariant mass, the diphoton transverse momentum, the azimuthal angle difference between the two photons, and the cosine of the polar angle in the Collins-Soper frame of the diphoton pair. Results are compared to theory predictions at leading, next-to-leading and next-to-next-to-leading order for diphoton production.