  We consider the possibility that the diphoton excess at 750 GeV is caused by
a new scalar resonance produced in photon fusion. This scenario is parametrised
by only one relevant effective couplings and is thus minimal. We show that this
setup can reproduce both the production rate and width of the resonance, and is
not in conflict with the 8 TeV limits on the diphoton cross section. The
scenario also predicts event rates for $WW$, $ZZ$, $Z\gamma$ final states. We
suggest to perform precision measurements by studying light-by-light scattering
with intact protons detected in forward detectors. We construct a simple model
that shows that the required couplings can be achieved with new vectorlike,
uncolored fermions (with a strong Yukawa coupling to the resonance) which may
also account for the required width.
