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

The antineutron-proton total doss section has been measured in the low mome ntum range 50-400 MeV/c (below 100 MeV/c for the first time). The measureme nt was performed at LEAR (CERN) by the OBELIX experiment, thanks to its uni que antineutron beam facility. A thick target transmission technique has be en used. The measured total cross section shows an anomalous behaviour belo w 100 MeV/c. A dominance of the isospin I = 0 channel over the I = 1 one at low energy is clearly deduced. (C) 2000 Elsevier Science B.V. All lights r eserved.