Observation of a Fine Structure in $e^{+}{e}^{-}\to$ hadrons Production at the Nucleon-antinucleon Threshold

Abstract

A study of hadron production at the nucleon-antinucleon threshold has been performed with the CMD-3 detector at the VEPP-2000 $e^{+}{e}^{-}$ collider. A very fast rise with about 1 MeV width has been observed in the $e^{+}{e}^{-}\to p\bar{p}$ cross section. A sharp drop in the $e^{+}{e}^{-}\to 3({\pi }^{+}{\pi }^{-})$ cross section has been confirmed and found to have a less than 2 MeV width, in agreement with the observed fast rise of the $e^{+}{e}^{-}\to p\bar{p}$ cross section. For the first time a similar sharp drop is demonstrated in the $e^{+}{e}^{-}\to K^{+}{K}^{-}{\pi }^{+}{\pi }^{-}$ cross section. The behavior of the $e^{+}{e}^{-}\to 3({\pi }^{+}{\pi }^{-}),K^{+}{K}^{-}{\pi }^{+}{\pi }^{-}$ cross sections cannot be explained by an interference of any resonance amplitude with continuum, therefore this phenomenon cannot be due to a narrow near-threshold resonance. No such structure has been observed in the $e^{+}{e}^{-}\to 2({\pi }^{+}{\pi }^{-})$ cross section.

arXiv comment7 pages, 5 figures

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