Every second, billions upon billions of incredibly low-mass subatomic particles called neutrinos shoot out of the Sun and glide undetected through your body.
These neutrinos are produced by the two known types of fusion reactions that occur on our Sun, and so far scientists have only detected one group of them: neutrinos produced by protons that come together to create helium.
But for the first time, physicists working on the Borexino experiment in Italy say they have finally observed the second most elusive group of ‘lost’ neutrinos.
This tiny handful of neutrinos is the result of a second helium recipe. They are known as ‘CNO neutrinos’, named for the Sun’s carbon-oxygen-nitrogen (CNO) cycle, and scientists have been searching for them for decades.
If we can find a better way to analyze them, we might be able to solve a major problem about our Sun: how much metal it actually contains.
“With this result, Borexino has completely unraveled the two processes that feed the Sun,” said physicist Gioacchino Ranucci of the Italian National Institute of Nuclear Physics in Milan, as reported by ScienceNews.
Ranucci presented the results at the Neutrino 2020 conference that was held virtually this week. It is important to note that the details have not yet been peer-reviewed, but the possibility is already drawing the interest of the physics community.
ANU experimental particle physicist Lindsey Bignell in Australia was not involved in the study, but was paying close attention to the results of the presentation.
“The measurements presented by the Borexino collaboration represent the culmination of a heroic effort to remove funds from its detector enough to measure CNO neutrinos,” Bignell told ScienceAlert.
“These results will be very important in understanding the nature of our Sun and may solve the problem of solar metallicity.”
Oddly enough, we can’t seem to determine how metal our Sun is, with predictions based on two different methods that disagree by around 28 percent. These CNO neutrinos could give us a casting vote on which model, if any, is correct.
The reason CNO neutrinos have been so difficult to find is because they are difficult to distinguish from the other types of neutrinos produced by our Sun, particularly with the background currents and temperature changes that result from the Borexino detector.
The experiment setup consists of a huge stainless steel sphere designed to capture the elusive flicker ofneutrinos when they collide with molecules of a solvent called pseudocumene. To avoid flickering with boring old radiation particles, the entire experiment is immersed in a tank of water. And then armored in rock.
A little less than 300 tons of solvent make up the core of the Borexino detector, so you imagine that everything would blink like a July 4th celebration.
But neutrinos only make themselves known through the weak nuclear force, forcing them to step inside an incredibly small window of 10 ^ -46 square centimeters to hope to shake the nucleus of an atom.
This means that despite being bathed in tiny particles, perhaps a few dozen neutrinos per day get close enough to have a chance of causing a light burst.
Experiments like this have been used to measure neutrino emissions since the 1960s, mapping distant cosmic explosions, nearby nuclear reactions, and the abundance of particles shining from the Sun.
Most of the neutrinos emitted by our nearest star were made as the hydrogen ions fused together to produce an alpha particle of helium, so it’s not surprising that decades of neutrino hunting have given us a good idea of that reaction. stellar in particular.
Borexino’s choice of solvent was adjusted to collect neutrinos that contained a specific hit, one that would allow him to focus on other types of nuclear reaction.
Since 2007, the experiment has recorded glimpses that can be traced back to the production of isotopes like beryllium-7 and boron-8, for example, helping researchers confirm the math behind the standard ‘zoo’ of particles.
But CNO neutrinos have been slightly more difficult to detect than the rest.
The CNO cycle is a convoluted alternative to the ‘proton plus proton’ method for making helium that uses carbon, oxygen and nitrogen as a series of steps.
Finding traces of the CNO cycle will help us better determine its limits and the Sun’s confusing combination of elements, especially when it comes to its role in the nucleosynthesis of other parts of the periodic table.
“The use of neutrinos is advantageous because it is not only an independent way of measuring solar metallicity, but it is the only technique that is directly sensitive to the metallicity of the Sun’s core,” says Bignell.
This study was presented at the Neutrino 2020 virtual conference.
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