Measurement of antineutron-proton total and annihilation cross sections from 100 to 500 MeV/c

Total and annihilation np cross sections from 100 to 500 MeV/c are reported, the first such measurements with good statistics in this momentum range. These cross sections are well represented by A+B/p, where p is the incident antineutron momentum, and are in agreement with previous np and pn measurements. A comparison of these cross sections with phenomenological potential model calculations is good overall. However, the microscopic quark model gives unsatisfactory predictions. The agreement between previous pp annihilation cross sections and np cross sections above 300 MeV/c is excellent. The total np cross section is lower than the total pp cross section in this momentum range. Both of these types of behavior are predicted by potential models. The anticipated availability of future pp data below 300 MeV/c should indicate whether these trends continue at lower momenta.