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 kilotonne-years .
For the hep neutrino search , two events are observed in the effective electron energy range of 14.3 MeV < \mathrm { T _ { \mathrm { eff } } } < 20 MeV where 3.1 background events are expected .
After accounting for neutrino oscillations , an upper limit of 2.3 \times 10 ^ { 4 } cm ^ { -2 } s ^ { -1 } 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 < \mathrm { T _ { \mathrm { eff } } } < 35 MeV and , consequently , an upper limit on the \nu _ { e } component of the DSNB flux in the neutrino energy range of 22.9 MeV < E _ { \nu } < 36.9 MeV of 70 cm ^ { -2 } s ^ { -1 } 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 two orders of magnitude on the previous upper limit on the \nu _ { e } component of the DSNB flux .