Diffraction dissociation of photons on hydrogen

We report results from a measurement of the inclusive diffraction dissociation of photons on hydrogen, {γ}p{→}Xp, in the range 75p_γ148 GeV/c, 0.02{}t{}0.1 (GeV/c)², and MX{}²$/s0.1. Our data show an exponential t dependence and a dominant 1/${M}X² behavior for MX{}²$>4 ${GeV}². We test the finite-mass sum rule and, by comparing γp with{{π}}^{{{-}}}$p data obtained in the same apparatus, we test factorization.