Neutrino induced coherent pion production

Understand

We discuss different parameterizations of the $C_5^A(q^2)$ $N\Delta$ axial form factor, fitted to the old Argonne bubble chamber data for pion production by neutrinos, and we use coherent pion production to test their low $q^2$ behavior.

• We find moderate effects that will be difficult to observe with the accuracy of present experiments.
• We also discuss the use of the Rein-Sehgal model for low energy coherent pion production.
• By comparison to a microscopic calculation, we show the weaknesses of some of the approximations in that model that lead to very large cross sections as well as to the wrong shapes for differential ones.