The rate of neutrino-electron elastic scattering interactions from 862 keV ${}^7\mathrm{Be}$ solar neutrinos in Borexino is determined to be $46.0\pm 1.5(\mathrm{stat}{)}_{-1.6}^{+1.5}(\mathrm{syst})\mathrm{\text{counts}}/(\mathrm{day}·100\mathrm{ton})$. This corresponds to a ${\nu }_e$-equivalent ${}^7\mathrm{Be}$ solar neutrino flux of $(3.10\pm 0.15)\times {10}^9{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ and, under the assumption of ${\nu }_e$ transition to other active neutrino flavours, yields an electron neutrino survival probability of $0.51\pm 0.07$ at 862 keV. The no flavor change hypothesis is ruled out at $5.0\sigma$. A global solar neutrino analysis with free fluxes determines ${\Phi }_{pp}={6.06}_{-0.06}^{+0.02}\times {10}^{10}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ and ${\Phi }_{\mathrm{CNO}}<1.3\times {10}^9{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ (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 $1\times {10}^{-2}\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$ after pulse shape discrimination. No signal is observed and a lower limit is derived for the half-life of neutrinoless double beta decay of ${}^{76}\mathrm{Ge}$, $T_{1/2}^{0\nu }>2.1\times {10}^{25}\mathrm{yr}$ (90% C.L.). The combination with the results from the previous experiments with ${}^{76}\mathrm{Ge}$ yields $T_{1/2}^{0\nu }>3.0\times {10}^{25}\mathrm{yr}$ (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 $49\pm 3_{\mathrm{stat}}\pm 4_{\mathrm{syst}}\mathrm{\text{counts}}/(\mathrm{day}·100\mathrm{ton})$. The hypothesis of no oscillation for ${}^7\mathrm{Be}$ solar neutrinos is inconsistent with our measurement at the $4\sigma$ C.L. Our result is the first direct measurement of the survival probability for solar ${\nu }_e$ 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 ${\nu }_e$, and the limit on the effective neutrino magnetic moment using solar neutrinos.