  Several models for physics beyond the Standard Model predict new particles
with a decay signature including hard photons and missing energy. Two
well-motivated examples are supersymmetry with gauge-mediated breaking (GMSB)
and the standard model with two universal extra dimensions.
  Both models lead to decay chains with similar collider signatures, including
hard photon emission. The main discriminating feature are the spins of the new
particles. In this paper we discuss how information about the spins of the
particles can be extracted from lepton-photon or quark-photon invariant mass
distributions at the Large Hadron Collider. The characteristic shapes of the
distributions are derived analytically and then studied in a realistic
Monte-Carlo simulation. We find that for a typical GMSB mass spectrum with
particle masses below 1 TeV, already 10 fb$^{-1}$ integrated luminosity at 14
TeV center-of-mass energy are sufficient to discriminate the two models with
high significance.
