Enhanced leading production of ${\mathit{D}}^{\pm }$ and ${\mathit{D}}^{\mathrm{*}\pm }$ in 250 GeV ${\mathrm{\pi }}^{\pm }$-nucleon interactions

A leading charm meson is one with longitudinal momentum fraction, ${\mathit{x}}_{\mathit{F}}$>0, whose light quark (or antiquark) is of the same type as one of the quarks in the beam particles. We report on the production asymmetry, A=[σ(leading-σ(nonleading)]/[σ(leading)+σ(nonleading)] as a function of ${\mathit{x}}_{\mathit{F}}$. The data consist of 1500 fully reconstructed ${\mathit{D}}^{\pm }$ and ${\mathit{D}}^{\mathrm{*}\pm }$ decays in Fermilab experiment E 769. We find a significant asymmetry for the production of charm quarks is not expected in perturbative quantum chromodynamics.