https://www1.cb.uni-bonn.de/fileadmin/user_upload/internal/Publication/Publication_PhysRept_413_2005_KlemptEtAl.pdf

The antinucleon-nucleon interaction at low energy: annihilation dynamics

We study the possibility of producing a new kind of nuclear system that in addition to ordinary nucleons contains a few antibaryons (B{sup -}=p{sup -},{lambda}{sup -}, etc.). The properties of such systems are described within the relativistic mean-field model by employing G-parity transformed interactions for antibaryons. Calculations are first done for infinite systems and then for finite nuclei from {sup 4}He to {sup 208}Pb. It is demonstrated that the presence of a real antibaryon leads to a strong rearrangement of a target nucleus, resulting in a significant increase of its binding energy and local compression. Noticeable effects remain even after the antibaryon coupling constants are reduced by a factor of 3-4 compared to G-parity motivated values. We have performed detailed calculations of the antibaryon annihilation rates in the nuclear environment by applying a kinetic approach. It is shown that owing to significant reduction of the reaction Q values, the in-medium annihilation rates should be strongly suppressed, leading to relatively long-lived antibaryon-nucleus systems. Multinucleon annihilation channels are analyzed too. We have also estimated formation probabilities of bound B{sup -}+A systems in p{sup -}A reactions and have found that their observation will be feasible at the future GSI antiproton facility. Several observablemore » signatures are proposed. The possibility of producing cold multi-quark-antiquark clusters is discussed.« less

Antibaryons bound in nuclei

Proton-antiproton annihilations at rest into π0ω, π0η, π0γ, π0π0, and π0η′

We report measurements of branching ratios for production of a series of two meson final states in
 
$$\bar p$$

 
p annihilations at rest in liquid hydrogen. We find:
 
$$\begin{gathered} BR(\bar pp \to \pi ^ + \pi ^ - ) = (3.07 \pm 0.13) \cdot 10^{ - 3} \hfill \\ BR(\bar pp \to K^ + K^ - ) = (0.99 \pm 0.05) \cdot 10^{ - 3} \hfill \\ BR(\bar pp \to \pi ^0 \pi ^0 ) = (6.93 \pm 0.43) \cdot 10^{ - 4} \hfill \\ BR(\bar pp \to \pi ^0 \eta ) = (2.12 \pm 0.12) \cdot 10^{ - 4} \hfill \\ BR(\bar pp \to \pi ^0 \omega ) = (5.73 \pm 0.47) \cdot 10^{ - 3} \hfill \\ BR(\bar pp \to \pi ^0 \eta ') = (1.23 \pm 0.13) \cdot 10^{ - 4} \hfill \\ BR(\bar pp \to \eta \eta ) = (1.64 \pm 0.10) \cdot 10^{ - 4} \hfill \\ BR(\bar pp \to \eta \omega ) = (1.51 \pm 0.12) \cdot 10^{ - 2} \hfill \\ BR(\bar pp \to \eta \eta ') = (2.16 \pm 0.25) \cdot 10^{ - 4} \hfill \\ BR(\bar pp \to \omega \omega ) = (3.32 \pm 0.34) \cdot 10^{ - 2} \hfill \\ BR(\bar pp \to \omega \eta ') = (0.78 \pm 0.08) \cdot 10^{ - 2} \hfill \\ \end{gathered}$$

 These are the first measurements of the channels ηη′ and ωη′ and in almost all the other channels are more precise than previous results. We also obtain, in a more precise fashion, the following ratios of branching ratios:K
+
K
−/π+π−=0.323±0.013, π0η′/π0η=0.548±0.056, ηη′/ηη=0.31±0.15, ωη′/ωη=0.515±0.040, π0η/π0π0=0.303±0.010, ηη/π0π0=0.232±0.011 and π0ω/ηω=0.377±0.12. The measurements are made for different η and η′ decays, and we thus obtain Γη→3π
0/Γη→γγ=0.841±0.034, and
 
$$\Gamma _{\eta ' \to \gamma \gamma } /\Gamma _{\eta ' \to \pi ^0 \pi ^0 \eta } = 0.091 \pm 0.009$$

 .

/pdf/antiproton-proton-annihilation-at-rest-into-two-body-final-5e3rhc7aly.pdf

M. Meyer

Papers

Proton-antiproton annihilations at rest into π0ω, π0η, π0γ, π0π0, and π0η′

A modular NaI(Tl) detector for 20–1000 MeV photons☆