2012: First evidence of pep solar neutrinos by direct detection in Borexino

First Evidence of pep Solar Neutrinos by Direct Detection in Borexino
G. Bellini et al. (Borexino Collaboration) M. Wójcik, G. Zuzel, M. Misiaszek
Phys. Rev. Lett. 108, 051302 (2012)

Download: http://prl.aps.org/abstract/PRL/v108/i5/e051302


We observed, for the first time, solar neutrinos in the 1.0-1.5 MeV energy range. We measured the rate of pep solar neutrino interactions in Borexino to be [3.1+-0.6(stat)+-0.3(syst)] counts/(day x 100 ton) and provided a constraint on the CNO solar neutrino interaction rate of <7.9 counts/(day x 100 ton) (95% C.L.). The absence of the solar neutrino signal is disfavored at 99.97% C.L., while the absence of the pep signal is disfavored at 98% C.L. This unprecedented sensitivity was achieved by adopting novel data analysis techniques for the rejection of cosmogenic 11C, the dominant background in the 1-2 MeV region. Assuming the MSW-LMA solution to solar neutrino oscillations, these values correspond to solar neutrino fluxes of [1.6+-0.3]x10^8 cm^-2s-1 and 7.7×10^8 cm^-2s-1 (95% C.L.), respectively, in agreement with the Standard Solar Model. These results represent the first measurement of the pep neutrino flux and the strongest constraint of the CNO solar neutrino flux to date.