W. Maneschg

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 ${\ensuremath{\Phi}}_{\mathrm{CNO}}<1.3\ifmmode\times\else\texttimes\fi{}{10}^{9}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ (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.

Neutrinoless double beta decay is a process that violates lepton number conservation. It is predicted to occur in extensions of the standard model of particle physics. This Letter reports the results from phase I of the Germanium Detector Array (GERDA) experiment at the Gran Sasso Laboratory (Italy) searching for neutrinoless double beta decay of the isotope $^{76}\mathrm{Ge}$. Data considered in the present analysis have been collected between November 2011 and May 2013 with a total exposure of 21.6 kg yr. A blind analysis is performed. The background index is about $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\text{ }\text{ }\mathrm{counts}/(\mathrm{keV}\text{ }\mathrm{kg}\text{ }\mathrm{yr})$ after pulse shape discrimination. No signal is observed and a lower limit is derived for the half-life of neutrinoless double beta decay of $^{76}\mathrm{Ge}$, ${T}_{1/2}^{0\ensuremath{\nu}}>2.1\ifmmode\times\else\texttimes\fi{}{10}^{25}\text{ }\text{ }\mathrm{yr}$ (90% C.L.). The combination with the results from the previous experiments with $^{76}\mathrm{Ge}$ yields ${T}_{1/2}^{0\ensuremath{\nu}}>3.0\ifmmode\times\else\texttimes\fi{}{10}^{25}\text{ }\text{ }\mathrm{yr}$ (90% C.L.).

We report the direct measurement of the $^{7}\mathrm{Be}$ solar neutrino signal rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The interaction rate of the 0.862 MeV $^{7}\mathrm{Be}$ neutrinos is $49\ifmmode\pm\else\textpm\fi{}{3}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{4}_{\mathrm{syst}}\text{ }\text{ }\mathrm{\text{counts}}/(\mathrm{day}\ifmmode\cdot\else\textperiodcentered\fi{}100\text{ }\text{ }\mathrm{ton})$. The hypothesis of no oscillation for $^{7}\mathrm{Be}$ solar neutrinos is inconsistent with our measurement at the $4\ensuremath{\sigma}$ C.L. Our result is the first direct measurement of the survival probability for solar ${\ensuremath{\nu}}_{e}$ in the transition region between matter-enhanced and vacuum-driven oscillations. The measurement improves the experimental determination of the flux of $^{7}\mathrm{Be}$, $pp$, and CNO solar ${\ensuremath{\nu}}_{e}$, and the limit on the effective neutrino magnetic moment using solar neutrinos.

We report the measurement of $\ensuremath{\nu}\mathrm{\text{\ensuremath{-}}}e$ elastic scattering from $^{8}\mathrm{B}$ solar neutrinos with 3 MeV energy threshold by the Borexino detector in Gran Sasso (Italy). The rate of solar neutrino-induced electron scattering events above this energy in Borexino is $0.22\ifmmode\pm\else\textpm\fi{}0.04(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.01(\mathrm{syst})\text{ }\text{ }\mathrm{cpd}/100\text{ }\text{ }\mathrm{t}$, which corresponds to ${\ensuremath{\Phi}}_{^{8}\mathrm{B}}^{\mathrm{ES}}=2.4\ifmmode\pm\else\textpm\fi{}0.4\ifmmode\pm\else\textpm\fi{}0.1\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$, in good agreement with measurements from SNO and SuperKamiokaNDE. Assuming the $^{8}\mathrm{B}$ neutrino flux predicted by the high metallicity standard solar model, the average $^{8}\mathrm{B}$ ${\ensuremath{\nu}}_{e}$ survival probability above 3 MeV is measured to be $0.29\ifmmode\pm\else\textpm\fi{}0.10$. The survival probabilities for $^{7}\mathrm{Be}$ and $^{8}\mathrm{B}$ neutrinos as measured by Borexino differ by $1.9\ensuremath{\sigma}$. These results are consistent with the prediction of the MSW-LMA solution of a transition in the solar ${\ensuremath{\nu}}_{e}$ survival probability ${P}_{ee}$ between the low-energy vacuum-driven and the high-energy matter-enhanced solar neutrino oscillation regimes.