Manifestation of the pion pole in pp → nn charge-exchange scattering

A recent experiment at LEAR, the CERN Low Energy Antiproton Ring, has provided very precise differential cross-section data for the pp → nn charge-exchange reaction. When performing the extrapolation procedure to the pion pole originally proposed by G.F. Chew the data exhibit the same dynamical mechanism than the np → pn line reversal reaction. The residue at the pole is consistent with the known value of the charged πNN coupling constant, as expected from charge conjugation invariance.