Anomalous Bumpy Structures in the Capture Cross Sections of Antiprotons by Helium

We investigate the state-specified capture process of antiprotons by helium. Freezing one of the two electrons, we reduce this four-body rearrangement problem into a three-body problem. The capture cross sections are calculated by solving the Chew-Goldberger-type integral equation. Differing from the capture of antiprotons by hydrogen atoms, the bumpy structures are revealed in the total angular momentum dependent capture cross sections. Further analysis shows that the bumps arise from the partial channel closing due to the removal of the energy degeneracy in the antiprotonic helium.

Figure 1

The $L$-dependent capture cross sections of antiprotons by helium at 10 eV incident energy.

Figure 2

The energy levels of antiprotonic helium. The horizontal dashed line is the total energy for 10 eV incident case.

Figure 3

The state-specified capture cross sections normalized to the total capture cross section for 10 eV incident energy.

Figure 4

The ejected electron energy distributions due to the capture of antiprotons by helium at different incident energies.

Figure 5

The total capture cross sections of antiprotons by helium atoms (solid curve) and hydrogen atoms (dashed curve). The capture cross sections by helium atoms (filled squares) and helium ions (open squares) calculated by the CTMC method [11, 13] are also plotted.