Charm hadroproduction with an impact parameter trigger

We report results on hadroproduction of charm based on a sample of ∼750 D mesons. Charmed particles, produced in a thin segmented target of Si and W by a 340 GeV/c π− beam and selected by a novel trigger with an enrichment factor of ∼15, are identified by the invariant mass of secondary vertices. Data were collected with the Ω’ spectrometer at the CERN SPS supplemented by a silicon microstrip vertex detector. Assuming the parameterization σ(π−N→DX∼Aα where A is the atomic number, we find α=0.89±0.05±0.05 for a data sample with an average xF of 0.2. The xF and p⊥ distributions of the charged D mesons are also described and the possibility of a leading effect is investigated.