HIGH-PRECISION MEASUREMENT OF THE P(P)OVER-BAR-]N(N)OVER-BAR CHARGE-EXCHANGE DIFFERENTIAL CROSS-SECTION

The differential pBARp --> nBARn change-exchange cross section has bee n measured at the CERN Low Energy Antiproton Ring (LEAR), at two incid ent pBAR momenta, 601 and 1202 MeV/c. The main features of the differe ntial cross-section near the forward direction, i.e. a sharp peak at 0 -degree scattering angle followed by an energy dependent dip-bump stru cture, are confirmed and measured with good precision and high statist ical accuracy. The data show very clearly that the shape of the cross- section is a manifestation of the pion-exchange amplitude, and a simpl e extrapolation to the pion pole already indicates that the pion-nucle on coupling constant f2c can be determined with good precision.