Isobar electroproduction as a background from interaction of beams with residual gas at φ-factories

It is shown that when beams interact with a residual gas at φ-factories the reaction of the electroproduction of the Δ(1232) isobar proceeds vigorously. The isobar decay gives ∼ 107 pions over an effective year of 107 s per meter of a residual gas. These pions are emitted largely across the beam axis with a resonance energy distribution at 265 MeV with a width 120 MeV in the isobar rest system. We present formulae for the distributions of the four-momentum transfer square, the angles, the energies and the momentum of the decay products, needed for the simulation of the process under consideration.