Valence quark annihilation effect on charmed meson production in pi N   collisions
  We discuss the hadroproduction of charmed mesons in the framework of the constituent cascade model taking into account the valence quark annihilation. It is shown that the small valence quark annihilation process dominates the leading particle production at large Feynman x and explains the recent experimental data on the asymmetry between D^0 and D^0 bar at 350 GeV/c. 
Tsutomu Tashiro, Hujio Noda, Kisei Kinoshita and Shin-ichi Nakariki