Antibaryons bound in nuclei

Abstract

We study the possibility of producing a new kind of nuclear system that in addition to ordinary nucleons contains a few antibaryons $(\stackrel{\ensuremath{-}}{B}=\stackrel{\ensuremath{-}}{p},\stackrel{\ensuremath{-}}{\ensuremath{\Lambda}}$, 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 $^{4}\mathrm{He}$ to $^{208}\mathrm{Pb}$. 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 $\stackrel{\ensuremath{-}}{B}+A$ systems in $\stackrel{\ensuremath{-}}{p}A$ reactions and have found that their observation will be feasible at the future GSI antiproton facility. Several observable signatures are proposed. The possibility of producing cold multi-quark-antiquark clusters is discussed.