  Among various models to explain the $750$ GeV diphoton resonance hinted at
the LHC Run 2, a class of models where the resonance decays not into a pair of
photons but into a pair of photon-jets is gathering definite attention. In this
paper, we study how well we can distinguish the di-photon-jet resonance from
the diphoton resonance by examining detector responses to the photon-jets. We
find that the sum of $p_T$ of the first $e^+e^-$ pair from the photon
conversion provides strong discrimination power. We also discuss determination
of the lifetime of the light intermediate particle by measuring the photon
conversion points.
