The nuclear physics program of ASACUSA is concerned with the measurements of antiproton-nuclei cross sections at low energies (from 5.3 MeV down to the 100 keV region). These measurements are expected to contribute to understand the dynamics of the annihilation process which is of interest for both nuclear physics and fundamental cosmology.
The initial phase of the experimental program has been devoted to measure for the first time the antiproton annihilation cross sections on medium-heavy and heavy nuclear targets at kinetic energy of 5.3 MeV. In Figure 1 the results achieved at the Antiproton Decelerator at CERN for Ni, SN and Pt targets are plotted with the existing measurements at energies below 500 MeV. It appears evident that at very low energies the present measurements are the only extending to the heavy nuclear targets range. Our results are consistent with the predictions from the black-disk model with the contribution of the Coulomb interaction between the antiproton and the nucleus at low energies.
Experimental limitations had prevented till now to achieve energies below the MeV region in spite of the interest they represent for theoretical models. Recently the ASACUSA Collaboration has succeeded for the first time in observing the antiproton-nucleus annihilation in the extremely low energy range of about 100 keV. The time distribution of the signals on C, Pd and Pt targets are shown in Figure 2. The used technique permits the measurement of the antiproton annihilation cross section and paves the road toward future measurements at the coming antiproton decelerator ring called ELENA at CERN.