Electron antineutrino search at the Sudbury Neutrino Observatory

Upper limits on the (ν) over bar (e) flux at the Sudbury Neutrino Observatory have been set based on the (ν) over bar (e) 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 (ν) over bar (e)'s from the Sun and other potential sources. Both differential and integral limits on the (ν) over bar (e) flux have been placed in the energy range from 4-14.8 MeV. For an energy-independent nu(e)-->(ν) over bar (e) conversion mechanism, the integral limit on the flux of solar (ν) over bar (e)'s in the energy range from 4-14.8 MeV is found to be Phi( nu e)less than or equal to3.4x10(4) cm(-2) s(-1) (90% C.L.), which corresponds to 0.81% of the standard solar model B-8 nu(e) flux of 5.05x10(6) cm(-2) s(-1), and is consistent with the more sensitive limit from KamLAND in the 8.3-14.8 MeV range of 3.7x10(2) cm(-2) s(-1) (90% C.L.). In the energy range from 4-8 MeV, a search for (ν) over bar (e)'s is conducted using coincidences in which only the two neutrons are detected. Assuming a (ν) over bar (e) spectrum for the neutron induced fission of naturally occurring elements, a flux limit of Phi((ν) over bare)less than or equal to2.0x10(6) cm(-2) s(-1) (90% C.L.) is obtained.