  We present a full next-to-leading order (NLO) QCD corrections to diphoton
production at the hadron colliders in both standard model and ADD model. The
invariant mass and rapidity distributions of the diphotons are obtained using a
semi-analytical two cut-off phase space slicing method which allows for a
successful numerical implementation of various kinematical cuts used in the
experiments. The fragmentation photons are systematically removed using
smooth-cone-isolation cuts on the photons. The NLO QCD corrections not only
stabilise the perturbative predictions but also enhance the production cross
section significantly.
