Isobar Electroproduction as a Background from Interaction of Beams with   Residual Gas at $\phi$-Factories
  It is shown that when beams interact with a residual gas at $\phi$-factories the reaction of the electroproduction of the $\Delta (1232)$ isobar proceeds vigorously. The isobar decay gives $\sim 10^7$ pions during an effective year of $10^7$ s per meter of a residual gas. These pions are emitted largely across the beam axis and have a resonance energy distribution with a peak nearby 265 MeV of a width close to 120 MeV in the isobar rest system. There are presented formulae for the distributions of the four-momentum transfer square, the angles, the energies and the momentum of the decay products, that is all required for the simulation of the process under consideration. 
M.N. Achasov (2), N.N. Achasov (1), V.B. Golubev (2), S.I. Serednyakov   (2) ((1) S.L. Sobolev Institute for Mathematics, No...