Coherent production of photons by neutrinos

The reaction ν+N→ν+N+γ, involving the coherent emission of a photon in a neutrino-nucleus collision, can produce “single shower” events that simulate the reaction ν+e→ν+e. The ratio of coherent photons to electrons (for an ²⁷Al target) is estimated to be 40% at E_ν=20GeV and 10% at E_ν=20 GeV. We examine the extent to which the “excess” of showers seen in the Aachen-Padova experiment could be understood by this mechanism.