Optical model potential analysis of n¯A and nA interactions

We use a momentum-dependent optical model potential to analyze the annihilation cross sections of the antineutron <(n) over bar> on C, Al, Fe, Cu, Ag, Sn, and Pb nuclei for projectile momenta P-lab less than or similar to 500 MeV/c. We obtain a good description of annihilation cross section data of Barbina et al. [Nucl Phys. A 612, 346 (1997)] and of Astrua et al. [Nucl Phys. A 697, 209 (2002)] which exhibit an interesting dependence of the cross sections on P-lab as well as on the target mass number A. We also obtain the neutron (n) nonelastic reaction cross sections for the same targets. Comparing the nA reaction cross sections sigma(nA)(rec) to the <(n)over5 bar>A annihilation cross sections sigma(ann'<(n) over bar>A) we find that ais significantly larger than sigma(ann) ((n) over barA), that is, the sigma((n) over barA)(ann)/sigma(nA)(rec) cross section ratio lies between the values of about 1.5 to 4.0 in the momentum region where comparison is possible. The dependence of the (n) over bar annihilation cross section on the projectile charge is also examined in comparison with the antiproton (p) over bar. Here we predict the <(p)>A annihilation cross section on the simplest assumption that both (p) over barA and (n) over barA interactions have the same nuclear part of the optical potential but differ only in the electrostatic Coulomb interaction. Deviation from a such simple model extrapolation in measurements will provide new information on the difference between (n) over barA and (p) over barA potentials.