Approximately 99 percent of solar energy emitted as neutrinos is generated by nuclear reaction sequences triggered by proton-proton (pp) fusion, in which hydrogen is converted to helium, say scientists like physicist Andrea Pocar of the University of Massachusetts Amherst. Today, they report on new results from Borexino, one of the most sensitive neutrino detectors on the planet, deep beneath the Italian Apennines
"Neutrons emitted by this chain are a unique tool for solar and neutrino physics," they explain , Her new work in Nature reports on "the first complete study of all components of the Borexino pp chain". These components include not only the pp neutrinos but also other beryllium 7 (7Be), Pep and boron 8 (8B) neutrinos. The pp fusion reaction of two protons to produce deuteron, deuterium nuclei, is the first step in a reaction sequence responsible for about 99 percent of solar energy, says Pocar.
He adds, "What's new today is incremental, it's not a jump, but it's the culmination of more than 1
" Borexino offers the best measurement for the pp, 7Be and Pep neutrinos, "he adds. "Other experiments measure the 8B neutrinos more precisely, but our lower threshold measurement agrees with them."
Next, "Once you have more accurate data, you can feed them back into the model of the sun behaves, then the model can be refined, and everything leads to a better understanding of the Sun: neutrinos have told us how the The sun is burning, and the sun has once again provided us with a unique source to study how neutrinos behave.Borexino, which is expected to run for another two to three years, has greatly enhanced our understanding of the sun. "
For previous studies of pp, 7B, pep and 8B neutrinos, the team had focused on them separately in targeted analyzes of the data collected in restricted energy windows, "such as trying to characterize a forest by taking a picture of many individual tree species", notices Pocar. "Several pictures give you an idea of a forest, but it's not the same as the photo of the entire forest."
"What we've done now is a single photograph that reflects the entire forest, the full spectrum of everything, the different neutrinos in one, instead of zooming in to look at small pieces, we all see it all at once Detector now so good, are confident and confident that our only shot applies to the entire spectrum of neutrino energies. "
Solar neutrinos are flowing at almost the speed of light from the star in the middle of our system, up to 420 billion people every square centimeter of the Earth's surface per second. Because they interact only through the weak nuclear force, they are virtually unaffected by matter, making it very difficult to detect and distinguish nuclear decay from common material, says Pocar.
The Borexino instrument detects neutrinos while interacting with the electrons of an ultrapure organic liquid scintillator in the center of a large sphere surrounded by 1,000 tons of water. Its great depth and many onion-like protective layers hold the nucleus as the least-radiation medium on the planet. He is the only detector on Earth that can observe the entire spectrum of the solar neutrino at the same time, which he has now achieved.
The physicist UMass Amherst, a principal investigator in a team of more than 100 scientists, is particularly interested in Now he focuses on measuring another type of solar neutrino, known as CNO neutrinos, which he hopes will be useful will be to address an important open question in stellar physics, namely the metallicity or metal content of the sun.
"There are two models that predict different levels of elements heavier than helium, which is metal to astronomers in the sun, lighter metallicity, and a heavier model," he notes. CNO neutrinos are emitted in a cyclic fusion reaction sequence that differs from the pp chain and subdominant in the Sun, but is considered to be the major source of stronger stars. The CNO neutrino flux is strongly influenced by solar metallicity.
Pocar says, "Our data may show a slight preference for heavy metallicity, so we'll investigate that because neutrinos from the sun, especially CNO, can help us unravel this."
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