Symmetric ${\pi }^{-}$ Production from $K^{+}+p\to {\pi }^{-}+$ Anything at 12 $\frac{\mathrm{GeV}}{c}$

The longitudinal momentum distribution of ${\pi }^{-}$ meson from the reaction $K^{+}+p\to {\pi }^{-}+$ anything at 11.8 $\frac{\mathrm{GeV}}{c}$ is examined in various reference frames. A forward-backward symmetry is found in that frame corresponding to a simple quark model. The frame of symmetry is dependent on the charged-particle multiplicity, however, which reduces the appeal of that model in explaining the present data.