Longitudinal- and Transverse-Momentum Distributions for<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:math>Mesons in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mn>18.5</mml:mn><mml:mo>−</mml:mo><mml:mfrac><mml:mrow><mml:mi mathvariant="normal">GeV</mml:mi></mml:mrow><mml:mrow><mml:mi>c</mml:mi></mml:mrow></mml:mfrac><mml:mi> </mml:mi><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>p</mml:mi></mml:math>Interactions

New data are presented on the longitudinal- and transverse-momentum spectra of ${\ensuremath{\pi}}^{\ensuremath{-}}$ mesons produced in both ${\ensuremath{\pi}}^{\ensuremath{-}}p$ and ${\ensuremath{\pi}}^{+}p$ interactions at 18.5 $\frac{\mathrm{GeV}}{c}$. These distributions are studied as a function of the number of charged particles observed in the final states. The spectra are discussed in terms of relevant models and are compared with similar data from $\mathrm{pp}$ interactions. The data cannot be factorized into a simple product of independent functions of longitudinal and transverse momentum. The distributions suggest strongly that a simple quark-quark model is inadequate to explain multipion production.