Observation of a fine structure in e+e− → 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. The very fast rise with about 1 MeV width has been observed in the e + e − → p p ¯ cross section. A sharp drop in the e + e − → 3 ( π + π − ) 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 − → p p ¯ cross section. For the first time a similar sharp drop is demonstrated in the e + e − → K + K − π + π − cross section. The behavior of the e + e − → 3 ( π + π − ) , K + K − π + π − 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 − → 2 ( π + π − ) cross section.