2020/06/30 by M. Agostini, K. Altenmüller, S. Appel +113 · 6 citations
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Dark Matter and Cosmic Phenomena #Neutrino Physics Research #acm:85-05 #astro-ph.IM #astro-ph.SR #hep-ex #msc:85-05 #physics.ins-det
paper · pdf · doi:10.1038/s41586-020-2934-0
43 pages, 14 figures
crossref issued 2020/11/25 · crossref published 2020/11/25 · crossref published-online 2020/11/25 · openalex publication_date 2020/11/25 · crossref created 2020/11/25 · crossref published-print 2020/11/26 · arxiv created 2021/07/22 · arxiv updated 2021/07/23 · crossref deposited 2023/05/20 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28 · crossref indexed 2026/08/03
For most of their existence stars are fueled by the fusion of hydrogen into helium proceeding via two theoretically well understood processes, namely the pp chain and the CNO cycle. Neutrinos emitted along such fusion processes in the solar core are the only direct probe of the deep interior of the star. A complete spectroscopy of neutrinos from the \it pp chain, producing about 99% of the solar energy, has already been performed \citebib:Nature-2018. Here, we report the direct observation, with a high statistical significance, of neutrinos produced in the CNO cycle in the Sun. This is the first experimental evidence of this process obtained with the unprecedentedly radio-pure large-volume liquid-scintillator Borexino detector located at the underground Laboratori Nazionali del Gran Sasso in Italy. The main difficulty of this experimental effort is to identify the excess of the few counts per day per 100 tonnes of target due to CNO neutrino interactions above the backgrounds. A novel method to constrain the rate of \bi contaminating the scintillator relies on the thermal stabilisation of the detector achieved over the past 5 years. In the CNO cycle, the hydrogen fusion is catalyzed by the carbon (C) - nitrogen (N) - oxygen (O) and thus its rate, as well as the flux of emitted CNO neutrinos, directly depends on the abundance of these elements in solar core. Therefore, this result paves the way to a direct measurement of the solar metallicity by CNO neutrinos. While this result quantifies the relative contribution of the CNO fusion in the Sun to be of the order of 1%, this process is dominant in the energy production of massive stars. The occurrence of the primary mechanism for the stellar conversion of hydrogen into helium in the Universe has been proven.