First real–time detection of solar pp neutrinos by Borexino

M Pallavicini,G Zuzel,B Caccianiga,C Ghiano,F Gabriele,M Gromov,D Bravo,R Saldanha,Q Meindl,K Fomenko,S Manecki,G Korga,L Papp,D Kryn,S Schönert,G Testera,K Otis,G Bellini,S Davini,L Perasso,An Ianni,S Marcocci,P Cavalcante,D Franco,M Obolensky,S Gazzana,G Bonfini,M Misiaszek,E Meroni,B Lehnert,F Von Feilitzsch,C Salvo,T Lewke,A Sotnikov,W Maneschg,R Tartaglia,A Pocar,Y Suvorov,A Caminata,A Razeto,D Bick,N Rossi,E Litvinovich,G Lukyanchenko,O Zaimidoroga,O Smirnov,A Ianni ,V Muratova,H Wang,M Skorokhvatov,P Lombardi,M Wójcik ,C Hagner,A Romani,P Mosteiro,V Kobychev,A Goretti,A Chepurnov,F Calaprice,M Giammarchi,A Empl,G Ranucci,M Laubenstein,M Meyer,S Sukhotin,Κ Zuber ,L Miramonti,S Zavatarelli,I Machulin,F Ortica,L Oberauer,M Montuschi,J Benziger,C Galbiati,E Hungerford,L Ludhová ,H Simgen,R B Vogelaar ,A Etenko,M Göger‐Neff ,D Korablëv,M Wurm,D D’angelo ,D Vignaud,J Winter,Á Chavarría ,A Derbin,A Re,M Kayser,F Lombardi

doi:10.1051/epjconf/201612101001

Abstract

Solar neutrinos have been pivotal to the discovery of neutrino flavour oscillations and are a unique tool to probe the reactions that keep the Sun shine. Although most of solar neutrino components have been directly measured, the neutrinos emitted by the keystone pp reaction, in which two protons fuse to make a deuteron, have so far eluded direct detection. The Borexino experiment, an ultra-pure liquid scintillator detector running at the Laboratori Nazionali del Gran Sasso in Italy, has now filled the gap, providing the first direct real time measurement of pp neutrinos and of the solar neutrino luminosity.

Highlights

The study of low energy solar neutrinos (i.e. below 1–2 MeV, see Fig. 1) is relevant for two main reasons: on one hand, they offer a unique opportunity to investigate the behaviour of the Sun’s interior and test the predictions of the Standard Solar Model; on the other, they allow to probe the MSW-LMA neutrino oscillation scenario in an energy range that is not accessible to water Cherenkov detectors [1, 2], which can detect solar neutrinos only above an energy threshold of about 3.5 MeV.The original main goal of Borexino [3, 4] was the precise measurement of the rate induced by the monochromatic electron neutrinos (0.862 keV) produced by the electron capture decay of 7Be in the Sun [5, 6]
In this paper we report about an even less anticipated result, namely the real time detection of the solar neutrinos of lowest energy, the so called pp neutrinos, which were detected in the early 90’s only by means of geochemical techniques [14], and its flux extracted indirectly
The 7Be rate was fixed to the rate previously obtained by Borexino [5]; CNO and pep rates were fixed to the values predicted by the highmetallicity Standard Solar Model; remaining background rates are left free in the fit, except for 214Pb, which is fixed to the value measured by looking at 214Bi-214Po coincidences

Summary

Introduction

The study of low energy solar neutrinos (i.e. below 1–2 MeV, see Fig. 1) is relevant for two main reasons: on one hand, they offer a unique opportunity to investigate the behaviour of the Sun’s interior and test the predictions of the Standard Solar Model; on the other, they allow to probe the MSW-LMA neutrino oscillation scenario in an energy range that is not accessible to water Cherenkov detectors [1, 2], which can detect solar neutrinos only above an energy threshold of about 3.5 MeV.The original main goal of Borexino [3, 4] was the precise measurement of the rate induced by the monochromatic electron neutrinos (0.862 keV) produced by the electron capture decay of 7Be in the Sun [5, 6]. The original main goal of Borexino [3, 4] was the precise measurement of the rate induced by the monochromatic electron neutrinos (0.862 keV) produced by the electron capture decay of 7Be in the Sun [5, 6].

Results

Conclusion