Antiproton annihilation on light nuclei at very low energies

Recent experimental data obtained bg the OBELIX collaboration on (p) over b ar D and (p) over bar(4)He total annihilation cross sections are analyzed. The combined analysis of these data with existing antiprotonic atom data al lows, fur the first time, the imaginary parts of the S-wave scattering leng ths for the tno nuclei to be extracted. The obtained values are: Im a(0)(sc ) = [-0.62 +/- 0.02(stat) +/- 0.04 (sys)] fro for (p) over bar D and Im a(0 )(sc) = [-0.36 +/- 0.03(stat)(-0.11)(+0.19) (sys)] fm for (p) over bar(4)He . Tills analysis indicates art unexpected behaviour of the imaginary part o f the (p) over bar-nucleus S-wave scattering length as: a function of the a tomic weight A: \Im a(0)(sc)\ ((p) over bar p) > \Im a(0)(sc)\ ((p) over bar D) > \Im a(0)( sc)\ ((p) over bar(4)He).