Neutrinos emitted in nuclear reactions (specifically beta processes) occurring in the core of the Sun provide us with a unique tool to study the details of the nuclear fusion processes occurring in our and other stars. The basic process fuses four protons into a He-4 nucleus with the emission of two positrons, two electrons neutrinos, and energy (some of which carried away as neutrino kinetic energy). In the Sun, Hydrogen-to-helium fusion occurs predominantly via the pp-chain, a set of reactions studied by Hans Bethe in the ’30s. Most recently, Borexino detected neutrinos from an alternative proton fusion mechanism, the CNO catalytic cycle also proposed in the ’30s by Bethe and Carl Friedrich von Weizsäcker.
Solar neutrinos were first detected by the Homestake radio-chemical experiment in the late ’60s and early 70s exploiting neutrino capture on Cl-37 contained in a large tank of dry cleaning fluid, leading to the 2002 Nobel Prize to Ray Davis. Other solar neutrino experiments include Kamiokande/SuperKamiokande (water Cherenkov detection, only B-8), Gallex/GNO/Sage (all, radiochemical on Gallium), SNO, and Borexino. All experiments detected many fewer solar neutrinos than expected, which led to the discovery that neutrinos, emitted by the sun with electron flavor, have largely converted to other flavors (muon to tau) when they are detected on earth. The experimental discovery of oscillations of atmospheric neutrinos (SuperK) and solar neutrinos (SNO) was recognized with the 2015 Nobel Prize to Takaaki Kajita and Art McDonald.
- A brief history of solar neutrinos by John Bahcall (link).
- An account of the solar neutrino puzzle by Raju Raghavan (link).
- Two presentations of the solar pp-chain with reference to Borexino’s measurement of pp, pep, Be-7, and B-8 neutrinos meant for a general audience (link1, link2).
- A presentation of the solar CNO-cycle with reference to Borexino’s measurement of CNO neutrinos meant for a general audience (link).
- A review paper on solar neutrinos (link).
Borexino is a 300-tonne organic liquid scintillator experiment that detects neutrinos in real time via their elastic scattering on electrons. It has operated since 2007 at the Laboratory Nazionali del Gran Sasso (LNGS) and measured all solar neutrino energy spectra, both in the pp-chain and the CNO cycle, many for the first time. Borexino is also one of two detectors (with KamLAND in Japan) that has measured geo-neutrinos, i.e. the antineutrinos from ?-decays of Th and U in the earth. It was preceded by a proof-of-principle 4-tonne prototype, the CTF, which proved that scintillator purities from radioactivity at and beyond one part in 1E16 were possible.
- “The Borexino Legacy – A Personal Account” – a remotely-delivered seminar at Case Western Reserve University, March 31, 2022 (link)
- “The Borexino closing act” – a remotely-delivered seminar on legacy and recent results of Borexino at Indiana University, April 22, 2022. (link)
- “The Borexino Legacy — from the solar neutrino puzzle to the detection of CNO solar neutrinos “- a seminar at Fermilab’s Neutrino University, July 7, 2022 (link)
? For a list of papers follow the “Publications” tab ?
NOTE: links are to the published, peer-reviewed version of each paper. In most cases, an open access version of each paper is available at arXiv.org.
