Precision Measurement of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mmultiscripts><mml:mi>Be</mml:mi><mml:mprescripts/><mml:none/><mml:mn>7</mml:mn></mml:mmultiscripts></mml:math>Solar Neutrino Interaction Rate in Borexino

Abstract

The rate of neutrino-electron elastic scattering interactions from 862 keV $^{7}\mathrm{Be}$ solar neutrinos in Borexino is determined to be $46.0\ifmmode\pm\else\textpm\fi{}1.5(\mathrm{stat}{)}_{\ensuremath{-}1.6}^{+1.5}(\mathrm{syst})\text{ }\mathrm{\text{counts}}/(\mathrm{day}\ifmmode\cdot\else\textperiodcentered\fi{}100\text{ }\text{ }\mathrm{ton})$. This corresponds to a ${\ensuremath{\nu}}_{e}$-equivalent $^{7}\mathrm{Be}$ solar neutrino flux of $(3.10\ifmmode\pm\else\textpm\fi{}0.15)\ifmmode\times\else\texttimes\fi{}{10}^{9}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ and, under the assumption of ${\ensuremath{\nu}}_{e}$ transition to other active neutrino flavours, yields an electron neutrino survival probability of $0.51\ifmmode\pm\else\textpm\fi{}0.07$ at 862 keV. The no flavor change hypothesis is ruled out at $5.0\text{ }\ensuremath{\sigma}$. A global solar neutrino analysis with free fluxes determines ${\ensuremath{\Phi}}_{pp}={6.06}_{\ensuremath{-}0.06}^{+0.02}\ifmmode\times\else\texttimes\fi{}{10}^{10}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ and ${\ensuremath{\Phi}}_{\mathrm{CNO}}&lt;1.3\ifmmode\times\else\texttimes\fi{}{10}^{9}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ (95% C.L.). These results significantly improve the precision with which the Mikheyev-Smirnov-Wolfenstein large mixing angle neutrino oscillation model is experimentally tested at low energy.