Neutrinos from the primary proton-proton fusion process in the Sun

• pp neutrinos constitute nearly the entirety of solar neutrino flux

• Secondary neutrinos observed. (Oscillation)

• pp neutrinos elude direct detection (pep neutrinos)

• Borexino Detector at San Grasso Laboratory (Italy)

• Observed pp neutrinos for the first time, confirming our understanding of the workings of our Sun

Sequence of nuclear fusion reactionsdefining the pp chain in the Sun

“Neutrinos from the primary proton-proton fusion process in the Sun” Borexino Collaboration, Nature 512, 383 (2014)

Energy Spectrum/Borexino Detector

• Solar Neutrino Energy Spectrum

• Fortunate energy spacing

• Carbon-14 Contamination

• Electron-Neutrino Elastic Scattering (Emax=264keV)

• Expected 131±2 counts per day per 100 ton

• 408 days of data• Actual 148±13 ±12

Neutrino Oscillation/Energy Spectra

• Neutrino Oscillation• Mikheyev-Smirnov-

Wolfenstein Large-Mixing-Angle solution (MSW-LMA)

• Different scattering cross sections

• Distinguishable at low energies (C-14 and pp)

• “Pile-up events”

• Future?