Antineutron-proton cross section from 50 to 400 MeV/c

The antineutron–proton total cross section has been measured in the low momentum range 50–400 MeV/c (below 100 MeV/c for the first time). The measurement was performed at LEAR-CERN by the OBELIX experiment, thanks to its unique antineutron beam facility. A thick target transmission technique has been used. The measured total cross section shows an anomalous behaviour below 100 MeV/c. A dominance of the isospin I=0 channel over the I=1 one at low energy is clearly deduced.