Weak pion production on nuclei

Neutrino oscillation experiments search a distortion in the neutrino flux at a detector positioned far away (L) from the source. By comparing near and far neutrino energy spectra, one gains information about the oscillation probability P(vi→vj = sin2 2θijsin2 Δ m2 ij L/2Ev, and then about the θij mixing angles and Δm2ij mass squared differences. In this moment new high quality data are available from MiniBoone, SciBoone and becoming from Miner experiments, full dedicated to measure cross sections. Charged current quasielastic scattering (CCQE) reaction vin→l-p on a single nucleon in the nucleus target is used as signal event. The neutrino energy is not directly measurable but has to be reconstructed from the reactions products through two body kinematics (exact only for free nucleons). However, competition with another processes could lead to a possible misidentification of the arriving neutrinos. In fact: 1.Disappearance searching experiments vμ→vx (like SciBoone) use vμnμ-p CCQE reaction to detect an arriving neutrino and reconstruct its energy. Nevertheless, Ev determination could be wrong for a fraction of background events vμp→μ-pπ+(CC1π+) that can mimic a CCQE event if the pion is absorbed in the target and/or not detected. 2. In vμ→ve appearance experiment (like MiniBooNE) one detects ve in an (almost) vμ beam. Signal event ven→ e-p is dominated by a vμN→vμNπ°,N = n p(NCLπ) background, and as the detector can not distinguish between e- and π° if one of both photons from the π°→γγ decay escapes, a misidentification is present. A precise knowledge of the cross sections of these elementary 1π charged (CC) neutrinonucleon, neutral current (NC) scattering processes and the inclusion of the several nuclear effects, is a prerequisite for the proper interpretation of the experimental data. This will allow to make simulations in event generators to eliminate fake events coming from 1π processes to get more realistic QE countings