Detecting the diffuse supernova neutrino background with LENA

Abstract

Low energy neutrino astronomy (LENA) has been proposed as a next generation 50 kt liquid scintillator detector. Its large target mass allows us to search for the diffuse supernova neutrino background (DSNB), which was generated by the cumulative emissions of all core-collapse supemovae throughout the Universe. Indistinguishable background from reactor and atmospheric electron antineutrinos limits the detection window to the energy range between 9.5 MeV and 25 MeV. Depending on the mean supernova neutrino energy, about 5 to 10 events per year are expected in this energy window. The background from neutral current reactions of atmospheric neutrinos surpasses the DSNB by more than one order magnitude, but can be suppressed by pulse shape discrimination. Assuming that the residual background is known with 5% uncertainty, the DSNB can be detected with 3cr significance after 10 years of data taking. In case no hint for a signal is seen, the allowed parameter space of DSNB models would be substantially constrained and the currently favored predictions for spectral mean energy and supernova rate would be excluded with more than 90% C.L.

Sensitivity to neutrino-antineutrino transitions for boron neutrinos

“…This cannot be ignored, and for this uncertainty we assign σ c = 13.6%. Usually in neutrino experiments background is well-known with relative error below 10% [24], however in this analysis we decided to vary the σ BKG up to 40% and investigate what influence this has on the result. Since we are interested in µ s and this parameter is unknown, then it is reasonable to equate n to the expected value of background b and to evaluate the upper limit for µ s .…”

“…• Atmospheric neutrinos through a neutral current (NC) interaction: High energy atmospheric neutrinos may collide with 12 C and eject a neutron which will imitate an IBD signal similarly to the fast neutron background. As demonstrated in [24], this background can be significantly decreased after searching for a coincident signal from the decay of a final isotope and using PSD.…”

“…This background with new energy windows is shown in the last row of Table 1. It should be emphasized that all values for NC background are presented after appropriate treatment as described in [24]. Approximation of the expected upper limits of signal and IBD-background for both types of experiments are shown in Figure 2.…”

Neutrino physics with accelerator driven subcritical reactors

“…[28]. The authors conclude that a pulse shape analysis can allow an 80% reduction in the NC background at the price of only 10% of the IBD signal.…”

“…About 40% create 11 C whose eventual decay can be used to veto this background [28], but the remaining background may be comparable to or somewhat larger than our signal in the 30 to 55 MeV regime of interest. It can be measured during beam-off periods, but nonetheless the statistical fluctuations in this background rate would provide a significant source of error if not vetoed.…”