Probing the exchanged object(s) in diffractive scattering
  The reaction mechanisms of the following proton diffractive scattering processes are studied and compared with one another: $\gamma^* p\to Vp,\gamma^* p\to Xp, pp\to (\Lambda K^+)p$ and $pA\to \Lambda K^+A$ (Here, $\gamma^*$ stands for the space-like photon in inelastic electron-proton scattering, $V$ for the vector mesons $\rho,\omega,\phi,J/\psi$, and $A$ for a target nucleus.) It is shown that, by taking parity, and C--parity conservation into account, the existing data for these reactions strongly suggest the following: A considerable part of the objects exchanged between projectile and target in the above-mentioned processes are virtual quark-antiquark pairs in color-singlet states with $J^{PC}=0^{-+}$, $I^G=0^+$, where $J$ stands for total angular momentum, $I$ for isospin, $P$, $C$ and $G$ stand for parity, C-parity and G-parity respectively. Such quark-antiquark pairs are created by soft-gluon interactions. New experiments are suggested; and predictions for such experiments are made. 
C. Boros (1), Liang Zuo-tang (1,2) and Meng Ta-chung (1) ((1) Institut   f\"ur theoretische Physik, Berlin, Germany (2) Depa...