Constraints on two-body axial currents from reactor antineutrino–deuteron breakup reactions

Abstract

We discuss how to reduce theoretical uncertainties in the neutrino–deuteron breakup cross-sections crucial to the Sudbury Neutrino Observatory's efforts to measure the solar neutrino flux. In effective field theory, the dominant uncertainties in all neutrino–deuteron reactions can be expressed through a single, common, isovector axial two-body current parameterized by L1,A. After briefly reviewing the status of fixing L1,A experimentally, we present a constraint on L1,A imposed by existing reactor antineutrino–deuteron breakup data. This constraint alone leads to an uncertainty of 6–7% at 7 MeV neutrino energy in the cross-sections relevant to the Sudbury Neutrino Observatory. However, more significantly for the Sudbury experiment, the constraint implies an uncertainty of only 0.7% in the ratio of charged to neutral current cross-sections used to verify the existence of neutrino oscillations, at the same energy. This is the only direct experimental constraint from the two-body system, to date, of the uncertainty in these cross-sections.