Measurement of the p̄ Annihilation Cross-Section at Very Low Energy

The knowledge of the antiproton-proton (pp) and antiprotonNuclear (pA) annihilation cross-section at very low energy (pp < 100 MeV/c) is of great interest for the understanding of the antinucleon-nucleon (NN) interaction. For instance, the low-energy limit (β → 0) of lim βσann is an important input for potential calculation and, if better known, may allow the existence of baryonia close to threshold to be ruled out or proved. Moreover, the measurement of partial-annihilation channels allows definite bounds to be put on the contribution of partial waves. Below 100 MeV/c annihilation and elastic scattering are the only possible reaction channels. In the following we discuss the possibility of extending annihilation cross-section measurements to energies as low as possible. For simplicity we consider only the case of a hydrogen target. For heavier targets the calculations are straightforward.