Neutrino Cross Section Measurements at T2K
Matthew Malek (left) gave a presentation of results made in T2K of neutrino cross section measurements. He started with an introduction to the experimental apparata, which have been described here in previous articles in the past days.
They can run both in neutrino and in antineutrino mode. The beams are 99% pure of muon neutrinos, with small contamination from other species (mostly muon antineutrinos). When run in antineutrino mode contaminations are slightly higher. The flux coming out of the beam is intercepted by the near detector, but as it gets to the far detector the energy distribution changes – there is a oscillation dip at 0.7 GeV. The nuclear effects are not insignificant, and must be taken into account to reduce systematics in most measurements.
Experimentally they cannot know the interaction mode, just the topology they see – and there is cross-talk between the corresponding categories. The goal of the on-axis cross section measurements is to disentangle these complicated cross-contaminations.
For CCQE events, by dividing the data into 1-track and 2-track, and at low and high energy, they can compare with previous experiments. (PRD 91:112002 (2015)). There is not the precision necessary to distinguish the different models so far.
Ingrid, the on-axis detector, has modules at different angle with respect to the beam direction. By looking at the data from the different modules, they get different energy distributions.This provides extension of the MINOS results on the cross section versus energy to lower energies. So far there is no disagreement between these datasets.
The analysis of off-axis data for CC events with no pion seems to show results in good agreement with prediction from models. The speaker also discussed other measurements of different topologies.
In summary, the T2K near detector suite can make precision cross section measurements as a supplement to its primary role in the oscillation analysis. Antineutrino cross-section measurements are being analyzed, and first results are starting to emerge.