Unified optical-model approach to low-energy antiproton annihilation on nuclei and to antiprotonic atoms

A successful unified description of (p) over bar nuclear interactions near E = 0 is achieved using a (p) over bar optical potential within a folding model, V-opt similar to <()over bar> * rho, where a <()over bar>p potential <()over bar> is folded with the nuclear density p. The potential v fits very well the measured pp-annihilation cross sections at low energies (p(L) < 200 MeV/c) and the 1s and 2p spin-averaged level shifts and widths for the (p) over barH atom. The density-folded optical potential V-opt reproduces satisfactorily the strong-interaction level shifts and widths over the entire periodic table, for A > 10, as well as the few low-energy (p) over bar -annihilation cross sections measured on Ne. Both <()over bar> and V-opt are found to be highly absorptive, which leads to a saturation of reaction cross sections in hydrogen and on nuclei. Predictions are made for (p) over bar -annihilation cross sections over the entire periodic table at these very low energies and the systematics of the calculated cross sections as function of A, Z and E is discussed and explained in terms of a Coulomb-modified strong-absorption model, Finally, optical potentials which fit simultaneously low-energy (p) over bar-He-4 observables for E < 0 as well as for E, 0 are used to assess the reliability of extracting Coulomb modified (p) over bar nuclear scattering lengths directly from the data. The relationship between different kinds of scattering lengths is discussed and previously published systematics of the (p) over bar nuclear scattering lengths is updated. (C) 2001 Elsevier Science B,V, All rights reserved.