  We studied the production of protons to the backward direction in (p,2p)
reactions on 6Li and 12C, accompanied by a proton emitted into the forward
hemisphere. The momenta of the final two protons were measured in a wide range
with the two-arm time-of-flight spectrometer. For each event we reconstructed
the mass of the intermediate off-shell particles. We have discovered a strong
narrow dip in the mass spectra of intermediate mesons at the mass of the real
pion.
