Spin analysis of S-channel diphoton resonances at the LHC

Abstract

The high mass neutral quantum states envisaged by theories of physics beyond the standard model can, at the hadron colliders, reveal themselves through their decay into a pair of photons. Once such a peak in the diphoton invariant mass distribution is discovered, the determination of its spin through the distinctive photon angular distributions is needed in order to identify the associated nonstandard dynamics. We discuss here the discrimination of the spin-2 Randall-Sundrum graviton excitation against the hypothesis of a spin-0 exchange giving the same number of events under the peak, by means of the angular analysis applied to resonant diphoton events expected to be observed at the LHC. The spin-0 hypothesis is modeled by an effective interaction of a high mass gauge singlet scalar particle interacting with the standard model fields. The basic observable of our analysis is the symmetrically integrated angular asymmetry A_CE, calculated for both graviton and scalar s-channel exchanges to next-to-leading order in QCD.