Neutrino Cross Section Models
Juan Nieves (right) discussed the basis of much of the measurements we nowadays do in all neutrino experiments around the world: the models predicting the cross section of neutrinos with matter. The quantitative impact of model variations in nuclear effects in the determination of oscillation parameters can be very significant.
One may consider the double differential cross section (in energy and angle), expressed in terms of the lepton and hadron tensor. The lepton tensor is well-known, while the hadron tensor can be parametrized in terms of structure functions. At high energy, the neutrino can resolve the internal structure of the target, and scatter not off nuclei but with quarks in the nucleon. DIS is the result, which manifests in the creation of a hadronic shower.
One thus of course needs the nucleon PDFs. There is some tension in the PDFs determined in charged lepton and neutrino interactions, and this should be kept in mind. DIS can also produce multipion and kaon final states; the respective cross sections are small but they play a role.
For quasi-elastic scattering, one had a puzzle. If one considered a W or Z absorption by a nucleon, the MiniBooNE CCQE data compared to the standard prediction evidenced a 20% difference. The solution was that in the data sample were included processes where the W was absorbed by a pair of interacting nucleons.
Very recently, T2K measured the CCQE-like cross sections, showing sizable uclear effects for all muon kinematics. Minerva also did something similar.
In conclusion, nuclear effects lead to sizable uncertainties on the cross section at low Q^2. It is important to incorporate these effect in event generators.