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.