Sensitivities of low energy reactor neutrino experiments

Abstract

The low energy part of the reactor neutrino spectra has not been measured experimentally. Its uncertainties limit the sensitivities in certain reactor neutrino experiments. This article discusses the origin of these uncertainties and examines their effects on the measurements of neutrino interactions with electrons and nuclei. The discrepancies between previous results and the Standard Model expectations can be explained by the under-estimation of the reactor neutrino spectra at low energies. To optimize the experimental sensitivities, measurements forν e -e cross-sections should focus on events with large (>1.5 MeV) recoil energy while those for neutrino magnetic moment searches should emphasize on events <100 keV. The merits and attainable accuracies for neutrino-electron scattering experiments using artificial neutrino sources are discussed.

Search of neutrino magnetic moments with a high-purity germanium detector at the Kuo-Sheng nuclear power station

“…Accuracies of better than 1.4% and 5% between calculations and measurements were achieved in the integrated [32] and differential [33] spectra. The evaluation of φ(ν e ) at energy below 2 MeV, on the other hand, is much more complicated [26]. Many input parameters remain unknown and there are no measurements to cross-check.…”

What can we learn from neutrino electron scattering?

“…Other isotopes such as 240 Pu and 242 Pu contribute to the flux at the O(0.1%) level and can be safely neglected. Combined with knowledge of the induced decay of these dominant isotopes by thermal neutrons, this procedure predicts the reactorν e energy spectrum to better than 10% and the total flux to nearly 1% [11]. Here, we will employ an empirical relation to describe the neutrino flux [12,13].…”

“…Some experiments do, in fact, use low energy reactor neutrinos; they are primarily designed to search for neutrino magnetic moments or study neutrino-nucleus coherent scattering [15]. The difficulty in working within this energy range is the uncertainty in the neutrino flux, which can be as large as 30% [11]. Flux measurements have not been made below ≈ 2MeV and theoretical calculations are not reliable due to an increase in the number of β-decay chains with low Q 2 values, many of which are not completely understood.…”

The Texono Research Program on Neutrino and Astroparticle Physics

“…It was recognized recently [10] that due to the uncertainties in the modeling of the low energy part of the reactor neutrino spectra, experiments to measure σ(SM) with reactor neutrinos should focus on higher electron recoil energies (T>1.5 MeV), while µ ν searches should base on measurements with T<100 keV. Observation of σ(coh) would require detectors with sub-keV sensitivities.…”