HomePhysicsA New Day Awaits Photo voltaic Neutrinos

A New Day Awaits Photo voltaic Neutrinos

• Physics 15, 194

Photo voltaic neutrinos are now not the “stars” of neutrino analysis, however next-generation experiments characterizing these neutrinos could deepen our understanding of photo voltaic and neutrino physics.

Borexino Collaboration

Neutrino experiments, such because the Borexino detector depicted on the best, have illuminated many particulars concerning the Solar and the neutrinos it produces.

Measurements of photo voltaic neutrinos proved that our star is powered by nuclear reactions and has dropped at mild many different particulars concerning the Solar’s inside workings. Additionally they led to the invention of neutrino oscillations—a phenomenon that’s troublesome to reconcile with established theories. Present neutrino analysis largely depends on neutrinos generated on Earth by reactors and accelerators. However some physicists argue that there’s nonetheless lots to be carried out with neutrinos generated within the Solar. A brand new era of solar-neutrino experiments could assist in fixing excellent questions on each neutrinos and photo voltaic physics, these scientists say.

The examine of photo voltaic neutrinos started within the late Sixties. Utilizing a detector crammed with dry-cleaning fluid and positioned in South Dakota’s Homestake gold mine, physicist Raymond Davis and his colleagues noticed the primary neutrino sign from the Solar. They have been shocked, nonetheless, to seek out that the variety of neutrinos was one third of what fashions predicted—a thriller that led to a “neutrino gold rush,” with many new experiments staking claims to totally different vitality and size scales associated to the neutrino conduct. Finally, physicists defined the lacking neutrinos as ensuing from oscillations between neutrino flavors (see Nobel Focus: Neutrino and X-ray Imaginative and prescient). These oscillations implied that neutrinos have mass, in rigidity with the usual mannequin of particle physics.

The examine of neutrino oscillations continues with efforts to pin down the neutrino plenty and mixing parameters that decide the oscillating conduct. The primary goal, nonetheless, is now not photo voltaic neutrinos. “Nearly all of the group, by a big margin, is concentrated on accelerator neutrinos,” says Michael Smy from the College of California, Irvine. The rationale for this shift, he says, is that an accelerator experiment can discover higher-energy neutrinos and management the source-detector distance over which oscillations could happen. Researchers also can change the accelerator on and off, which helps take away sure backgrounds.

On the flip facet, there are benefits to utilizing photo voltaic neutrinos. For one, the interactions between neutrinos and detector supplies are typically higher understood on the low energies that characterize photo voltaic neutrinos, Smy says. Photo voltaic neutrinos additionally come to us for “free,” so the experiments may be inexpensive, says Wick Haxton from College of California, Berkeley.

Many experiments have centered on photo voltaic neutrinos. The Borexino experiment in Italy, for instance, was constructed with the principle function of amassing low vitality (sub-MeV) neutrinos from the Solar. Because the undertaking’s begin in 2007, the crew has taken a number of steps to take away massive radioactive backgrounds. “Through the years, they’ve truly mapped the entire spectrum of photo voltaic neutrinos,” Haxton says. “They have been distinctive in that regard.” This week, the Borexino Collaboration reported observations of the neutrinos from the carbon-nitrogen-oxygen (CNO) cycle (see Viewpoint: Elemental Accounting of the Photo voltaic Inside).

Borexino shut down in October 2021, leaving a niche within the detection functionality of solar-neutrino research. “We should not have extra knowledge to be analyzed, and due to this fact the CNO result’s the final main output from our experiment,” says Borexino spokesperson Gioacchino Ranucci. The observations of the solar-neutrino spectrum have agreed effectively with solar-model predictions, and the info have positioned necessary constraints on oscillation parameters. “However there are nonetheless inquiries to be solved” relating to each the Solar’s chemical make-up and “tensions” within the neutrino oscillation image, says Ranucci.

Haxton sees a missed alternative within the closing of Borexino with out a clear substitute. “There’s some fascinating questions concerning the Solar that we haven’t answered very effectively,” he says. Borexino demonstrated, for instance, that solar-neutrino observations may assist resolve uncertainties concerning the elemental abundances within the inside of the Solar. However extra exact measurements might be wanted to find out the preliminary elements out of which the Solar fashioned, Haxton says. He additionally want to see a greater accounting of the whole vitality in photo voltaic neutrinos, which could reveal unique physics occurring contained in the Solar. Present neutrino detectors can’t present these measurements, as they’re solely delicate to the high-energy finish of the solar-neutrino spectrum.

Nonetheless, there are a number of solar-neutrino issues that present and deliberate detectors can sort out. Smy works on Japan’s Tremendous-Kamiokande (Tremendous-Ok) experiment, which has been instrumental in understanding neutrinos because it started taking knowledge in 1996. It continues to be a workhorse in neutrino physics, observing neutrinos from the Solar and different sources. Smy says that Tremendous-Ok’s present solar-neutrino analysis focuses on the matter impact—a neutrino taste conversion that happens in extremely dense areas, similar to the inside of the Solar and of Earth. The matter impact has already been noticed, however Smy and his colleagues proceed to investigate Tremendous-Ok knowledge within the vitality area the place the matter impact activates, as this transition could comprise indicators of nonstandard interactions between neutrinos and different particles.

One other focus of ongoing solar-neutrino analysis is pinpointing the values for the neutrino oscillation parameters. “There are attention-grabbing discrepancies within the knowledge that we very a lot need to resolve,” says Shirley Li from Fermi Nationwide Accelerator Laboratory (Fermilab) in Illinois. She is very focused on an obvious disagreement between solar-neutrino observations and reactor-neutrino observations. She has checked out whether or not this drawback may very well be resolved by the Deep Underground Neutrino Experiment (DUNE)—a deliberate neutrino detector within the Sanford Underground Analysis Facility (positioned within the former Homestake Mine the place Davis carried out his neutrino experiment). DUNE’s essential purpose is to look at high-energy neutrinos coming from the Fermilab accelerator. However the detector must also have the ability to detect photo voltaic neutrinos on the high-energy finish of the photo voltaic spectrum, in accordance with an evaluation by Li and her colleagues.

Along with DUNE, different deliberate neutrino tasks may present new solar-neutrino outcomes. Smy mentions Jiangmen Underground Neutrino Observatory (JUNO), a big neutrino detector in China that’s anticipated to begin taking knowledge subsequent 12 months. JUNO has the aptitude to detect each neutrinos from the Solar and antineutrinos from nuclear reactors. As such, it may take a look at so-called CPT symmetry that assumes a mirror-like relation between matter and antimatter. Additional down the highway, researchers are proposing to put in a neutrino experiment within the China Jinping Underground Laboratory, the deepest scientific facility on this planet. “They’ve the aptitude of constructing a Borexino-like detector that’s an order of magnitude bigger,” Haxton says. He thinks such an experiment may probably fill in a few of the lacking items to our understanding of the Solar.

The present lull in solar-neutrino physics could also be a product of the sooner pleasure surrounding the lacking neutrino drawback. “Of us have been so anxious to unravel the final drawback that—as soon as it was solved—they moved on to one thing else,” Haxton says. However he’s optimistic that solar-neutrino physics may have its day once more. “Physics goes in cycles.”

–Michael Schirber

Michael Schirber is a Corresponding Editor for Physics Journal primarily based in Lyon, France.


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