A Search for Neutrinos from the SolarhepReaction and the Diffuse Supernova Neutrino Background with the Sudbury Neutrino Observatory

Abstract

A search has been made for neutrinos from the hep reaction in the Sun and from the diffuse supernova neutrino background ( DSNB) using data collected during the first operational phase of the Sudbury Neutrino Observatory, with an exposure of 0.65 ktons yr. For the hep neutrino search, two events are observed in the effective electron energy range of 14:3 MeV < T eA < 20 MeV, where 3.1 background events are expected. After accounting for neutrino oscillations, an upper limit of 2:3 ; 10 4 cm À2 s À1 at the 90% confidence level is inferred on the integral total flux of hep neutrinos. For DSNB neutrinos, no events are observed in the effective electron energy range of 21 MeV < T eA < 35 MeV, and, consequently, an upper limit on the e component of the DSNB flux in the neutrino energy range of 22:9 MeV < E < 36:9 MeVof 70 cm À2 s À1 is inferred at the 90% confidence level. This is an improvement by a factor of 6.5 on the previous best upper limit on the hep neutrino flux and by 2 orders of magnitude on the previous upper limit on the e component of the DSNB flux.

Precise Determination of the UnperturbedB8Neutrino Spectrum

“…There the flux is dominated by neutrinos from the þ decay of 8 B, with a small contribution (about 3 orders of magnitude lower) by neutrinos produced in the 1 H þ 3 He reaction (''hep'' neutrinos). The latter was calculated theoretically [9] and seems to be in good agreement with the observational upper limit [10]. The unperturbed 8 B neutrino spectrum, however, is still under discussion.…”

“…However, they will influence the interpretation of the solar neutrino data in the next years, especially with an improvement in the solar neutrino statistics at energies above 14 MeV. The deviations have consequences on the upper limit on the solar hep neutrino signal and the diffuse supernova neutrino background [10], and the extension of the spectrum to higher neutrino energies leads to an improved determination of the 8 B neutrino background that dominates direct detection experiments searching for dark matter particles [30].…”

Neutrinos from failed supernovae at future water and liquid argon detectors

“…These are limited to handful of events from SN1987A [1,2], which was the only recent supernova close enough for its neutrino flux to be detectable. While the rarity of nearby supernovae seems an insurmountable problem, a new phase of data taking is expected to begin with the detection of the diffuse supernova neutrino flux (or background, DSNB), on which only upper limits exist [3][4][5][6]. Tiny but continuous in time, the diffuse flux will give tens to hundreds of events in a few years at future Mt scale detectors, ensuring constant progress for decades.…”

Upper limits on the diffuse supernova neutrino flux from the SuperKamiokande data

“…Among the direct limits on ν e , the strongest is from the search for charged current (CC) scattering on deuterium (ν e +d → p + p + e − ) at the Sudbury Neutrino Observatory (SNO), in the interval 22.9 − 36.9 MeV of neutrino energy [19]. The result is:…”