Antinucleon–nucleon interaction at low energy: scattering and protonium

Proton-antiproton scattering and annihilation into two mesons☆

Partial-wave analyses (PWAs) have a long history in the fields of πN and NN scattering. Due to the poor quality of low-energy antiproton beams and the resulting absence of accurate experimental data, analogous model-independent studies of the much more complex \(\bar pp\) system have in the past always been impossible. In recent years, however, experimental progress has been very significant, in particular due to the coming in 1983 of the Low-Energy Antiproton Ring (LEAR) facility at CERN. While in the pre-LEAR era spin-dependent observables and charge-exchange (\(\bar pp \to \bar nn\)) data were almost nonexistent, the situation between 400 and 925 MeV/c is now quite good: the LEAR collaborations PS172, PS173, PS198, and PS199 have measured a variety of observables with impressive accuracy. High-quality analyzing-power data have been obtained for the elastic [1] and charge-exchange [2] reactions. Very recently, even charge-exchange depolarization data have become available [3]. Unfortunately, the practical difficulties involved in constructing a high-quality “cooled” antiproton beam of lower momentum are large. Consequently, the \(\bar pp\) database below about 400 MeV/c is still by far not as good as one would like, in striking contrast to the pp case where very accurate data exist as low as T L = 0.35 MeV (P L = 25 MeV/c). It also remains an outstanding experimental challenge to construct a polarized antiproton beam to further probe the spin structure of the interaction.

https://arxiv.org/pdf/nucl-th/9403011.pdf

Antiproton-proton partial-wave analysis below 925 mev/c

Antinucleon-nucleon and antinucleon-nucleus interaction. A review of experimental data

Low-energy antiproton-neon interaction

Total and annihilation cross sections for p-barp and p-bard have been measured over the momentum range 355--1066 MeV/c at closely spaced momenta and with good energy resolution. No evidence is seen for the narrow structure reported by other experiments in the vicinity of 500 MeV/c. The present measurements indicate a broader enhancement in this region, which, if interpreted as a resonance, would have a height of approx. 3 mb and a width of approx. 20 MeV. This structure appears only in the p-barp data.

R.D. Tripp

Papers

Search for the S meson