Evidence for the onset of color transparency in ρ0 electroproduction off nuclei.

We have measured the nuclear transparency of the incoherent diffractive process in 12C and 56Fe targets relative to 2H using a 5 GeV electron beam. The nuclear transparency, the ratio of the produced ʼs on a nucleus relative to deuterium, which is sensitive to ρA interaction, was studied as function of the coherence length (), a lifetime of the hadronic fluctuation of the virtual photon, and the four-momentum transfer squared (). While the transparency for both 12C and 56Fe showed no dependence, a significant dependence was measured, which is consistent with calculations that included the color transparency effects.