Experimental Study of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>A</mml:mi></mml:math>Dependence of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mfrac><mml:mrow><mml:mi>J</mml:mi></mml:mrow><mml:mrow><mml:mi>ψ</mml:mi></mml:mrow></mml:mfrac></mml:math>Photoproduction

We have studied the photoproduction of $\frac{J}{\ensuremath{\psi}}$ 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, ${A}^{\ensuremath{\alpha}}$, we find that ${\ensuremath{\alpha}}_{\mathrm{coh}}=1.40\ifmmode\pm\else\textpm\fi{}0.06\ifmmode\pm\else\textpm\fi{}0.04$ for the coherent diffractive signals and ${\ensuremath{\alpha}}_{\mathrm{incoh}}=0.94\ifmmode\pm\else\textpm\fi{}0.02\ifmmode\pm\else\textpm\fi{}0.03$ for the incoherent signals.