The nature of the narrow peaks in the $e^+e^-$ pair production in heavy   ion collisions
  Experiments on heavy ion collisions performed at GSI (Darmstadt, Germany) revealed series of narrow quasi-equidistant peaks in the energy distribution of the produced $e^+e^-$ pairs in the range from 1.5 to 2.0 MeV which are ascribed to the pair coupling with a strong magnetic field generated by fast nuclei with $Z\sim90$. The pair is captured in the magnetic trap with dimensions of $10^{-10}$ cm and average field $\sim 5 \cdot 10^{12}$ Gs and, in turn, confines this magnetic field in the trap during $\sim 10^{-19}$ s due to the Alfven effect of magnetic field "freezing-in" into the conducting medium. 
P. I. Fomin, R. I. Kholodov
hep-ph