05 v 2 5 N ov 1 99 9 Antiproton annihilation on light nuclei at very low energies

The recent experimental data obtained by the OBELIX group on p̄D and p̄He 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 = [−0.62±0.02(stat)±0.04(sys)] fm for p̄D and Im a 0 = [−0.36± 0.03(stat) −0.11(sys)] fm for p̄ He. This analysis indicates an unexpected behaviour of the imaginary part of the p̄-nucleus Swave scattering length as a function of the atomic weight A: |Im a 0 | (p̄p) > |Im a 0 | (p̄D) > |Im a 0 | (p̄He). PACS numbers: 25.43.+t, 36.10−k Submitted for publication to the European Physical Journal A