Electron antineutrino search at the Sudbury Neutrino Observatory

Abstract

Upper limits on the ${\overline{\ensuremath{\nu}}}_{e}$ flux at the Sudbury Neutrino Observatory have been set based on the ${\overline{\ensuremath{\nu}}}_{e}$ 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 ${\overline{\ensuremath{\nu}}}_{e}$'s from the Sun and other potential sources. Both differential and integral limits on the ${\overline{\ensuremath{\nu}}}_{e}$ flux have been placed in the energy range from 4--14.8 MeV. For an energy-independent ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\overline{\ensuremath{\nu}}}_{e}$ conversion mechanism, the integral limit on the flux of solar ${\overline{\ensuremath{\nu}}}_{e}$'s in the energy range from 4--14.8 MeV is found to be ${\ensuremath{\Phi}}_{{\overline{\ensuremath{\nu}}}_{e}}\ensuremath{\le}3.4\ifmmode\times\else\texttimes\fi{}{10}^{4}\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ (90% C.L.), which corresponds to 0.81% of the standard solar model $^{8}\mathrm{B}$ ${\ensuremath{\nu}}_{e}$ flux of $5.05\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$, and is consistent with the more sensitive limit from KamLAND in the 8.3--14.8 MeV range of $3.7\ifmmode\times\else\texttimes\fi{}{10}^{2}\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ (90% C.L.). In the energy range from 4--8 MeV, a search for ${\overline{\ensuremath{\nu}}}_{e}$'s is conducted using coincidences in which only the two neutrons are detected. Assuming a ${\overline{\ensuremath{\nu}}}_{e}$ spectrum for the neutron induced fission of naturally occurring elements, a flux limit of ${\ensuremath{\Phi}}_{{\overline{\ensuremath{\nu}}}_{e}}\ensuremath{\le}2.0\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ (90% C.L.) is obtained.