Direct Measurement of the Pion Valence-Quark Momentum Distribution, the Pion Light-Cone Wave Function Squared

We present the first direct measurements of the pion valence-quark momentum distribution which is related to the square of the pion light-cone wave function. The measurements were carried out using data on diffractive dissociation of $500\mathrm{GeV}/c$ ${\pi }^{-}$ into dijets from a platinum target at Fermilab experiment E791. The results show that the $|q\overline{q}〉$ light-cone asymptotic wave function describes the data well for $Q^2\sim 10(\mathrm{GeV}/c{)}^2$ or more. We also measured the transverse momentum distribution of the diffractive dijets.