Optical model potential analysis of n¯A and nA interactions

In this study, we use a momentum-dependent optical model potential to analyze the annihilation cross sections of the antineutron $\overline{n}$ on C, Al, Fe, Cu, Ag, Sn, and Pb nuclei for projectile momenta p_lab ≲ 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 σ$\frac{nA}{rec}$ to the $\overline{n}A$ annihilation cross sections σ^{$\overline{n}A$}_ann, we find that σ^{$\overline{n}A$}_ann is significantly larger than σ$\frac{nA}{rec}$, that is, theσ^{$\overline{n}A$}_ann / σ$\frac{nA}{rec}$ 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 $\overline{n}$ annihilation cross section on the projectile charge is also examined in comparison with the antiproton $\overline{p}$. Here we predict the $\overline{p}A$ annihilation cross section on the simplest assumption that both $\overline{p}A$ and $\overline{n}A$ interactions have the same nuclear part of the optical potential but differ only in the electrostatic Coulomb interaction. Finally, deviation from a such simple model extrapolation in measurements will provide new information on the difference between $\overline{n}A$ and $\overline{p}A$ potentials.