 The Borexino detector, a hyper-sensitive instrument deep underground in Italy, has finally succeeded at the nearly impossible task of detecting CNO neutrinos from our sun’s core. These little-known particles reveal the last missing detail of the fusion cycle powering our sun and other stars, and could answer still-outstanding questions about the sun’s composition. Credit: Borexino Collaboration |
In the results published on November 26, 2020, in the journal Nature (and featured on the cover), researchers from the Borexino collaboration identified this rare type of neutrino as "ghost particles", the first to go unnoticed. Most cases go by clue.
The neutrinos were detected by a boraxino detector in a massive underground experiment in central Italy. Under the grant supervision shared by Frank Calapris, professor of physics at Princeton, the National Science Foundation in the United States supports the multinational project; Alumna Andrea Poker, a 2003 graduate of Princeton and professor of physics at the University of Massachusetts-Amherst; And Bruce Vogelar, professor of physics at the Virginia Polytechnic Institute and State University (Virginia Tech).
The diagnosis of the "ghost particle" confirms 1930s estimates that our sun's energy would be produced by a series of reactions involving carbon, nitrogen, and oxygen (CNO). This reaction produces less than 1% of the Sun's energy, but is considered the primary energy source in large stars. This process releases two neutrinos - the lightest basic cells of matter - as well as other sub-atomic cells and energy. Processes that are more abundant for hydrogen-to-helium fusion release neutrinos, but their spectral signatures vary, allowing scientists to distinguish between them.
"Confirmation of CNO burning in our sun, which only works at the 1% level, strengthens our confidence that we understand how stars work," said Calclapris and researchers from Borexino.
CNO neutrinos: Windows into the sun
For most of their lives, wires are fueled by hydrogen fuses in helium. In stars like our Sun, it is mainly through proton-proton chains. However, in heavy and hot wires, carbon and nitrogen catalyze hydrogen burning and release CNO neutrinos. Discovering any neutrino helps us to work inside the sun; When the boraxino detector discovered proton-proton neutrinos, this news provoked the scientific world.
CNO neutrinos not only confirm that the CNO process works in the Sun, they also help solve an important open question in astrophysics: the interior of the Sun is made up of "metals", which defines any element of astrophysics. Is heavier than hydrogen or helium and whether the "metallicity" of the core corresponds to the sun's surface or outer layers.
Unfortunately, neutrinos are very difficult to measure. More than 400 billion of them are ide every second inch of the Earth's surface, although in reality these "ghost cells" travel through the entire planet without communicating with anyone, making it too big for scientists to spot them and forcing one to use very carefully guarded equipment.
The Borexino detector is located half a mile below the Appenin Mountains in Italy, at the Najnili del Gran Sasso (LNGS) laboratory of the National Institute of Nuclear Physics in Italy, where a large belly balloon - about 30 feet - 300 tons ultra. Happened. -Pure liquid hydrocarbons are housed in a submersible multi-layer spherical chamber. A small fraction of the neutrons passing through the planet bounce electrons into these hydrocarbons, creating a beam of light that can be detected by a photon sensor flashing the water tank. Great depth, size and accuracy make Borexino a truly unique detector for this type of science.
The Borexino project at the University of Milan was started in the 1990s by a team of physicists led by Calapris, Gianpolo Bellini and the late King Raghavan (then at Bell Labs). Over the past 30 years, researchers around the world have assisted in discovering the proton-proton chain of neutrinos, and about five years ago, the team began the hunt for CNO neutrinos.
Suppressing the background
“It’s about suppressing the radioactive background for the last 30 years,” Calpris said.
Most of the neutrinos discovered by boraxino are proton-proton neutrinos, but only a few recognizable CNO neutrinos. Unfortunately, CNO neutrinos are similar to cells generated by the radioactive decay of polonium-210, which leaks isotope from a large nylon balloon. Separating the sun's neutrinos from polonium pollution requires a painstaking effort led by Princeton scientists, which began in 2014. Since radiation from the balloon could not be prevented from escaping, scientists have found another solution, ignoring the signals from the contaminated exterior. Protecting the deep inside of the shells and balloon. This is necessary to dramatically reduce the velocity of the fluid in the balloon. Most fluid flow is driven by thermal differences, so the U.S. team worked hard to achieve a very stable temperature profile for tanks and hydrocarbons so that the fluid is still possible. Temperature was accurately mapped by temperature probes set up by the Vogelar-led Virginia Tech Group.
"If this speed could be significantly reduced, we could see five or less energy repetitions per day caused by CNO neutrinos," Calapris said. "For reference, a cubic foot of 'fresh air', which is a thousand times denser than hydrocarbon liquids - experiences 100,000 radioactive decks per day, mostly from radon gas."
To ensure fluid stability, Princeton and Virginia tech scientists and engineers developed hardware to insulate the detector - especially a large blanket to wrap it around - in 2014 and 2015, then they made three pairs of heating circuits that have a perfectly constant temperature. They were successful in controlling the detector's temperature, but seasonal temperature changes in Hall C, where Borexino is located, still remain small liquid streams, obscuring the CNO signal.
So the two Princeton engineers, Antonio de Ludovico and Lidio Pitrophasia, teamed up with LNGS staff engineer Graziano Panella, Hall C. Air maintains a constant air temperature. The Active Temperature Control System (ATCS), finally developed in 2019, produces sufficient thermal stability inside and outside the balloon to cool currents and inside the detector, eventually contaminating the isotopes from the balloon walls to the core of the detector. Kept from being taken inside.
“The data is getting better and better”
Prior to the discovery of the CNO neutrino, the laboratory planned to complete the boraxino operation by the end of 2020. Now, data aggregation is likely to increase in 2021.
The amount of hydrocarbons at the heart of the boraxino detector has been increasing since February 2020, when data were collected for Nature Paper. This means that without exposing the CNO neutrino, which is the subject of this week's Nature article, it now has the potential to help solve the "metallic" problem - the question of whether the sun's core, outer layers and surface are all the same is a concentration of elements heavier than helium or hydrogen.
"We continue to collect data as we continue to improve core accuracy, focusing on the true potential of the metal." "Not only are we still collecting data, the data is getting better and better."
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