  The lighter top squark in supersymmetry can live long enough to form hadronic
bound states if it has no kinematically allowed two-body decays that conserve
flavor. In this case, scalar stoponium may be observable through its diphoton
decay mode at the CERN Large Hadron Collider, enabling a uniquely precise
measurement of the top-squark mass. The viability of the signal depends
crucially on the branching ratio to diphotons. We compute the next-to-leading
order QCD radiative corrections to stoponium annihilation decays to hadrons,
photons, and Higgs scalar bosons. We find that the effect of these corrections
is to significantly decrease the predicted branching ratio to the important
diphoton channel. We also find a greatly improved renormalization-scale
dependence of the diphoton branching ratio prediction.
