Far out cosmology: found neutrinos from the sun (Introduction)

by David Turell , Friday, November 27, 2020, 21:55 (1247 days ago) @ David Turell

Two different reactions seen:

https://www.nature.com/articles/d41586-020-03238-9?utm_source=Nature+Briefing&utm_c...

"...the Borexino Collaboration1 reports results that blast past a milestone in neutrino physics. They have detected solar neutrinos produced by a cycle of nuclear-fusion reactions known as the carbon–nitrogen–oxygen (CNO) cycle. Measurements of these neutrinos have the potential to resolve uncertainties about the composition of the solar core, and offer crucial insights into the formation of heavy stars.

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"Fusion reactions in the Sun produce an astonishing number of neutrinos: roughly 100 billion solar neutrinos pass through each of your thumbnails every second. Because of the weakness of their interactions, they are barely deterred from their path even when they have to pass through the entire body of the Earth: cutting-edge experiments5 (see also go.nature.com/36sktyj) have struggled to observe a difference in the measured neutrino flux between daytime and night-time, owing to the vanishingly small scale of this effect.

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"The Sun is powered by fusion reactions that occur in its core: in the intense heat of this highly pressurized environment, protons fuse together to form helium. This occurs in two distinct cycles of nuclear reactions. The first is called the proton–proton chain (or pp chain), and dominates energy production in stars the size of our Sun. The second is the CNO cycle, which accounts for roughly 1% of solar power, but dominates energy production in heavier stars.

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"The Borexino Collaboration now reports another groundbreaking achievement from its experiment: the first detection of neutrinos from the CNO cycle. This result is a huge leap forward, offering the chance to resolve the mystery of the elemental composition of the Sun’s core. In astrophysics, any element heavier than helium is termed a metal. The exact metal content (the metallicity) of a star’s core affects the rate of the CNO cycle. This, in turn, influences the temperature and density profile — and thus the evolution — of the star, as well as the opacity of its outer layers.

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"The Borexino experiment detects light produced when solar neutrinos scatter off electrons in a large vat of liquid scintillator — a medium that produces light in response to the passage of charged particles. A precise measurement of the energy and time profile of the detected light allows the scintillation caused by solar neutrinos to be differentiated from light resulting from other sources, such as radio-active contamination in the scintillator itself and in surrounding detector components."

Comment: Everything is so complex it takes many years of experimental refinement to get reliable results.