The main part of coherent pion production by neutrinos on nuclei is essentially determined by PCAC, provided that the leptonic momentum transferred square Q 2 remains sufficiently small. We give the formulas for the charged and neutral current cross sections, including also the small non-PCAC transverse current contributions and taking into account the effect of the µ − -mass. Our results are compared with the experimental ones and other theoretical treatments.
I. INTRODUCTIONCoherent production of pions by neutrinos has been studied by many experimental groups and measurements have been made for neutrino energies ranging from 2 to 80 GeV [1,2,3,4,5,6,7,8]. The main characteristics of such cross sections is that the energy of the recoiling nucleus and the invariant momentum transfer to it, always remain very small. A characteristic signature of these events is a sharp peak in the low |t| region. In addition to this, all experiments have observed that the momentum transfer from the leptonic sector Q 2 also remains very small, sharply peaking at Q 2 0.2 GeV 2 ; while the dependence of the cross section on the neutrino energy appears logarithmic at high energies.However, problems with the existence of the coherence phenomenon might appear at the lower energies used for the new oscillation experiments K2K, MiniBoone, MINOS etc. In particular, a new measurement by the K2K group at an average neutrino energy E 1 = 1.3 *