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 GeV/c π^- into dijets from a platinum target at Fermilab experiment E791. The results show that the \|qq¯> light-cone asymptotic wave function describes the data well for Q²~10 \(GeV/c\)² or more. We also measured the transverse momentum distribution of the diffractive dijets.