Structure of Nucleons at Small Distances

We report here the observation of surprisingly simple behaviors in the massive-hadron-pair ($m>\mathrm{}2\mathrm{}$ GeV) production from proton-nucleon collisions. With a 28.6-GeV incident proton beam and a pair spectrometer to detect the hadrons, the measured cross section decreases like $\frac{d^2\sigma }{\mathrm{dxdm}}\propto e^{-5m}$ and can be grouped into three groups: ${\pi }^{-}+p$; ${\pi }^{+}+{\pi }^{-}$, $\overline{p}+p$, $K^{-}+p$; and $K^{-}+{\pi }^{+}$, ${\pi }^{+}+p$. Within a given group the yield is the same to ±20%; different groups are separated by a factor of ∼ 10 from each other.