Antiproton annihilation on light nuclei at very low energies

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: $Im a^{sc}_0 = [- 0.62 pm 0.02 ({stat}) pm 0.04 ({sys})] fm$ for $bar{p}$D and $Im a^{sc}_0 = [- 0.36pm 0.03({stat})^{+0.19}_{-0.11}({sys})] fm$ 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: $|Im a^{sc}_0|$ ($bar{p}$p) > $|Im a^{sc}_0|$ ($bar{p}$D) > $|Im a^{sc}_0|$ ($bar{p}^4$He).