Isobar Electroproduction as a Background from Interaction of Beams with Residual Gas at phi-Factories

It is shown when interacting beams with a residual gas at phi-factories the reaction of the electroproduction of the $\Delta (1232)$ isobar proceeds vigorously and the isobar decay gives $\sim 10^7$ pions having a resonance energy distribution with a peak nearby 265 MeV and with a width close to 120 MeV, emitted largely across the beam axis, during an effective year of 10^7 s per meter of the interaction. There are presented formulae for the distributions of the four-momentum transfer square, the angles, the energies and the momentum of the decay products, everything required for the simulation of the process under consideration.