Pion Structure as Observed in the Reaction<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup></mml:mrow><mml:mi>N</mml:mi><mml:mo>→</mml:mo><mml:mrow><mml:msup><mml:mrow><mml:mi>μ</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow><mml:mrow><mml:msup><mml:mrow><mml:mi>μ</mml:mi></mml:mrow><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup></mml:mrow><mml:mi>X</mml:mi></mml:math>at 80 GeV/<i>c</i>

The production of ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ pairs with large longitudinal momentum has been studied in ${\ensuremath{\pi}}^{\ensuremath{-}}N$ collisions. The data confirm an earlier result that most of the pair production takes place via longitudinally polarized virtual photons as ${x}_{\mathrm{F}}\ensuremath{\rightarrow}1$. The transverse-momentum distribution of the muon pairs shows a marked narrowing in the same limit. The distribution of valence quarks in the pion is extracted, and indicates a nonzero probability of having a single quark carry all available longitudinal momentum. These results are compared with a QCD model of pion structure which includes the effect of higher-twist corrections.