Atomic mass dependence of [ital D][sup [plus minus]] and [ital D][sup 0],[ital [bar D]] [sup 0] production in 250 GeV [pi][sup [plus minus]]-nucleon interactions

We measure the relative cross sections for [ital D] mesons produced in interactions of [pi][sup [minus]] and [pi][sup +] beams with targets of Be, Cu, Al, and W. The measurement is based on 1400 fully reconstructed decays of the types [ital D][sup 0][r arrow][ital K][sup [minus]][pi][sup +], [ital D][sup +][r arrow][ital K][sup [minus]][pi][sup +][pi][sup +], and charge conjugates. We find that the cross section for the production of both neutral and charged [ital D]'s by either [pi][sup [minus]] or [pi][sup +] is well fitted by the form [ital A][sup [alpha]] where [ital A] is the atomic mass and [alpha]=1.00[plus minus]0.05[plus minus]0.02, where the errors are statistical and systematic, respectively. There is no significant dependence of [alpha] on the transverse or longitudinal momentum of the [ital D] meson or on the charge of either the incident pion or the produced [ital D] mesons.