Electron antineutrino search at the Sudbury Neutrino Observatory

Upper limits on the νₑ flux at the Sudbury Neutrino Observatory have been set based on the νₑ charged-current reaction on deuterium. The reaction produces a positron and two neutrons in coincidence. This distinctive signature allows a search with very low background for νₑ's from the Sun and other potential sources. Both differential and integral limits on the νₑ flux have been placed in the energy range from 4--14.8 MeV. For an energy-independent νₑ→νₑ conversion mechanism, the integral limit on the flux of solar νₑ's in the energy range from 4--14.8 MeV is found to be ${{Φ}}_{{{{ν}}}ₑ}{≤}3.4×{}{10}⁴ {cm}^{{-}2} {s}^{{-}1}$ (90% C.L.), which corresponds to 0.81% of the standard solar model $⁸B$ ${{ν}}ₑ$ flux of $5.05×{}{10}⁶ {cm}^{{-}2} {s}^{{-}1}$, and is consistent with the more sensitive limit from KamLAND in the 8.3--14.8 MeV range of $3.7×{}{10}² {cm}^{{-}2} {s}^{{-}1}$ (90% C.L.). In the energy range from 4--8 MeV, a search for ${{{ν}}}ₑ$'s is conducted using coincidences in which only the two neutrons are detected. Assuming a ${{{ν}}}ₑ$ spectrum for the neutron induced fission of naturally occurring elements, a flux limit of ${{Φ}}_{{{{ν}}}ₑ}{≤}2.0×{}{10}⁶ {cm}^{{-}2} {s}^{{-}1}$ (90% C.L.) is obtained.