Neutrino-nucleus interactions for oscillation experiments

6 problems

• Nucleon axial form factor: lattice QCD versus deuterium-target data

  Contested

  How strongly a neutrino scatters off a single proton or neutron depends on a function called the axial form factor, which describes the nucleon's weak-charge distribution. Lattice QCD (computer simulations of the strong force) gives a form factor that falls off more slowly than old bubble-chamber data on deuterium suggest.

• Can nuclear uncertainties bias DUNE and Hyper-Kamiokande CP-phase measurements?

  Open

  DUNE (Deep Underground Neutrino Experiment) and Hyper-Kamiokande will compare how neutrinos and antineutrinos change type to look for a difference between matter and antimatter. If the nuclear models wrongly predict how neutrinos and antineutrinos interact, the measured asymmetry could be shifted.

• Multinucleon and final-state effects in neutrino energy reconstruction

  Open

  Oscillation experiments must reconstruct each neutrino's energy from the particles leaving the nucleus, but some energy goes into undetected neutrons, knocked-out nucleons or reabsorbed pions. The bias this causes must be known to about one percent and is not.

• Electron- to muon-neutrino cross-section ratio on argon and oxygen

  Open

  Far detectors look for electron neutrinos but near detectors mostly measure muon neutrinos, so the experiments rely on theory for the ratio of the two collision rates. Small nuclear effects that depend on the lepton mass could change this ratio by a few percent.

• Reliable models of neutrino pion production on nuclei

  Contested

  In the few-GeV range many neutrino collisions make a pion, often through a short-lived excited nucleon called the Delta. Measurements from different experiments and the models used to describe them do not agree, especially for slow pions and small momentum transfers.

• Size and shape of multinucleon (2p2h) neutrino cross sections

  Open

  A neutrino can strike a correlated pair of nucleons at once instead of a single one, knocking out two particles. Different models of this two-nucleon process disagree on how often it happens by up to a factor of about two.