Abstract
Neutrinos emitted in the carbon, nitrogen, oxygen (CNO) fusion cycle in the Sun are a sub-dominant, yet crucial component of solar neutrinos whose flux has not been measured yet. The Borexino experiment at the Laboratori Nazionali del Gran Sasso (Italy) has a unique opportunity to detect them directly thanks to the detector’s radiopurity and the precise understanding of the detector backgrounds. We discuss the sensitivity of Borexino to CNO neutrinos, which is based on the strategies we adopted to constrain the rates of the two most relevant background sources, pep neutrinos from the solar pp-chain and ^{210}Bi beta decays originating in the intrinsic contamination of the liquid scintillator with ^{210}Pb. Assuming the CNO flux predicted by the high-metallicity Standard Solar Model and an exposure of 1000 days times 71.3 t, Borexino has a median sensitivity to CNO neutrino higher than 3 sigma . With the same hypothesis the expected experimental uncertainty on the CNO neutrino flux is 23%, provided the uncertainty on the independent estimate of the ^{210}text {Bi} interaction rate is 1.5 hbox {cpd}/100~hbox {ton} . Finally, we evaluated the expected uncertainty of the C and N abundances and the expected discrimination significance between the high and low metallicity Standard Solar Models (HZ and LZ) with future more precise measurement of the CNO solar neutrino flux.
Highlights
The Sun releases energy mainly through a nuclear fusion process known as the proton–proton chain
A detailed sensitivity study was performed which showed that if the backgrounds are constrained, the bulk of the sensitivity to the CNO neutrino signal can be established with a simple counting analysis
The statistical uncertainty on the CNO rate depends on the uncertainty in the determination of the pep neutrinos and 210Bi backgrounds
Summary
The Sun releases energy mainly through a nuclear fusion process known as the proton–proton chain (pp chain). The measurement of CNO neutrinos would allow the evaluation of the efficiency of the CNO cycle, helping with the determination of the age of globular clusters [5] It would provide a direct reading of the metal abundance in the solar core, which would in turn allow the study of the chemical evolution paradigm assumed by the standard solar model (SSM) [6]. 5 we comment on the relevance of the measurement of the flux of CNO neutrinos in the context of solar physics, with an emphasis on the “solar metallicity (or abundance) problem” This scientific puzzle originated when a re-determination of the surface metallicity of the Sun [9,10,11,12,13] indicated a lower value than previously assumed [14].
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