Observation of Color-Transparency in Diffractive Dissociation of Pions

We have studied the diffractive dissociation into dijets of $500\mathrm{GeV}/c$ pions scattering coherently from carbon and platinum targets. Extrapolating to asymptotically high energies (where $t_{\min }\to 0$), we find that when the per-nucleus cross section for this process is parametrized as $\sigma ={\sigma }_0{A}^{\alpha }$, $\alpha$ has values near 1.6, the exact result depending on jet transverse momentum. These values are in agreement with those predicted by theoretical calculations of color-transparency.