Antiproton annihilation on light nuclei at very low energies

Abstract

The recent experimental data obtained by the OBELIX group on $\bar{p}$D and ${\bar{p}}^4$He total annihilation cross sections are analyzed. The combined analysis of these data with existing antiprotonic atom data allows, for the first time, the imaginary parts of the S-wave scattering lengths for the two nuclei to be extracted. The obtained values are: $Im{a}_0^{sc}=[-0.62\pm 0.02(stat)\pm 0.04(sys)]fm$ for $\bar{p}$D and $Im{a}_0^{sc}=[-0.36\pm 0.03(stat{)}_{-0.11}^{+0.19}(sys)]fm$ for ${\bar{p}}^4$He. This analysis indicates an unexpected behaviour of the imaginary part of the $\bar{p}$-nucleus S-wave scattering length as a function of the atomic weight A: $|Im{a}_0^{sc}|$ ($\bar{p}$p) > $|Im{a}_0^{sc}|$ ($\bar{p}$D) > $|Im{a}_0^{sc}|$ (${\bar{p}}^4$He).

13 pages, 5 figures