Size and shape of multinucleon (2p2h) neutrino cross sections
In plain words
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.
Precise statement
Determine the two-particle-two-hole (2p2h) charged-current cross section from meson-exchange currents and short-range correlations on 12C, 16O and 40Ar, double-differential in muon momentum and angle for $E_{\nu}=0.5\ \text{to}\ 5\,\mathrm{GeV}$, to 10 percent, together with its neutrino versus antineutrino difference and its proton-proton versus neutron-proton final-state composition. Existing microscopic models (for example Nieves et al., Martini et al., SuSAv2) disagree in normalization and in the energy-transfer distribution.
What would settle it
An ab initio or microscopic calculation of 2p2h responses consistent with electron-scattering data in the dip region and with exclusive neutrino data on two-proton final states from argon and carbon detectors.