Physicists in Italy Discover Rare Particles Generated by a Fusion Process Inside the Sun

After a series of observations, scientists have, for the first time ever, discovered some rare, ghostly particles generated by a rather peculiar type of fusion inside our star, the Sun.​

The particles, called CNO-produced neutrinos, traveled from the Sun to a detector located deep underneath a mountain in Italy, which let physicists know about the peculiarity. This finding brings humans one step closer to learning more about the torrid nuclear reactions fueling our home star.

“With this outcome,” physicist Gioacchino Ranucci, a researcher at Italy’s National Institute for Nuclear Physics in Milan, says. “Borexino has completely unraveled the two processes powering the Sun.”

Observing a Rare Kind of Nuclear Fusion

Two kinds of nuclear fusion reactions take place in the Sun’s nucleus. The first, and most common, is the proton-proton fusion, where protons merge to transform hydrogen into helium. Researchers believe that such responses produce 99 percent of the Sun’s energy. At times, nuclear fusion can happen via a six-step process, known as the CNO cycle, where hydrogen is merged with helium to create carbon (C), nitrogen (N), and oxygen (O).

Overview of the CNO-I Cycle. [Image: Wikipedia]
Proton-proton fusion and the CNO-cycle generate different types of neutrinos, which are subatomic particles almost without a mass, and which can pass through ordinary matter without a clue of their presence, at least most of the time. Physicists regularly find neutrinos generated during the proton-proton process.

Still, on June 23rd, at the Neutrino 2020 Virtual Meeting, researchers from Italy’s Borexino detector revealed that they had found CNO-produced solar neutrinos for the very first time.

The Borexino Detector and How it Found the Signals

The underground Borexino Experiment, located at the Laboratori Nazionali del Gran Sasso, close to the town of L’Aquila, Italy, was created to analyze these extremely rare neutrino engagements. The Borexino​ detector includes a tank of about 60 feet (18 meters) tall that contains 280 tons (254 metric tons) of scintillating liquid, which flashes a light when electrons in the liquid respond to a neutrino. A bright flash, which shows higher energy, is more probable to come from CNO-generated neutrinos.

Buried deep beneath the ground and sheltered in a water tank, Borexino​’s core tank is lined with sensitive detectors that are incredibly isolated from background radiation from cosmic rays present all over Earth‘s surface. Without this cocooning, other signals would overpower the rare signatures coming from CNO neutrinos.

The Borexino Detector and its components. [Image: Laboratori Nazionali del Gran Sasso]
Ranucci also mentions the ‘unprecedented purity’ of the scintillating liquid, crediting it with much of the research’s success.

Further Studies Will Uncover More on the Sun’s Composition

Comparing the discovered CNO neutrino studies with the number of observed proton-proton neutrinos will help researchers reveal how much of the Sun is made up of elements heavier than hydrogen, like carbon, nitrogen, and oxygen.

The current outcome, even though not yet peer-reviewed and published in a scientific journal, showed a significance greater than five sigma with a greater than 99 percent confidence level, which means there is just one in a 3.5 million chance that the signal was generated by random fluctuations, rather than the CNO process. That doesn’t mean, however, that an alternative theory could not explain the data.

The Borexino international collaboration has researchers from Italy, France, Germany, Poland, Russia, as well as from three universities from the United States: Princeton, Virginia Tech, and the University of Massachusetts at Amherst.

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