Experimental Study of theADependence ofJψPhotoproduction

We have studied the photoproduction of $\frac{J}{\psi }$ mesons on H, Be, Fe, and Pb targets using real photons at a mean energy of 120 GeV. The $p_T^2$ spectra were used to separate the coherent diffractive signals from the incoherent signals. Parametrizing the per-nucleus cross sections in terms of power-law dependences, $A^{\alpha }$, we find that ${\alpha }_{\mathrm{coh}}=1.40\mathrm{}\pm 0.06\pm 0.04$ for the coherent diffractive signals and ${\alpha }_{\mathrm{incoh}}=0.94\mathrm{}\pm 0.02\pm 0.03$ for the incoherent signals.