James Vary is waiting for nuclear physics experiments to confirm the reality of a “tetraneutron” that he and his colleagues first theorized, predicted and announced during a presentation in the summer of 2014, followed by a research paper in the fall of 2016.
“Whenever we come up with a theory, we always have to say that we’re waiting for experimental confirmation,” said Vary, a professor of physics and astronomy at Iowa State University.
In the case of four neutrons (very, very) briefly joined together in a temporary quantum state or resonance, that day for Vary and an international team of theorists is now here.
The recently announced experimental discovery of a tetraneutron by an international group led by researchers at the Technical University of Darmstadt in Germany opens the door to further research and could lead to a better understanding of how the universe is formed. This exotic new state of matter may also have useful properties in existing or emerging technologies.
Neutrons, you probably remember from science class, are uncharged subatomic particles that combine with positively charged protons to form the nucleus of an atom. Individual neutrons are not stable and after a few minutes they convert to protons. Combinations of double and triple neutrons also do not form what physicists call resonance, a state of matter that is temporarily stable before decaying.
Enter the tetraneutron. Using the supercomputing power of Lawrence Berkeley National Laboratory in California, theorists calculated that four neutrons could form a resonant state with a lifetime of just 3×10-22 seconds, less than a billionth of a billionth of a second. It’s hard to believe, but it’s enough time for physicists to study.
Theorists’ calculations say that the tetraneutron must have an energy of about 0.8 million electron volts (a common unit of measurement in high energy and nuclear physics – visible light has energies of about 2 to 3 electron volts). ). of peak energy plotted showing a tetraneutron would be about 1.4 million electron volts. Theorists published subsequent studies that indicated that the energy would likely be between 0.7 and 1.0 million electron volts, while the width would be between 1.1 and 1.7 million electron volts. This sensitivity arose from the adoption of different candidates available for the interaction between neutrons.
A newly published article in the journal Nature reports that experiments at the Radioactive Isotope Beam Factory at the RIKEN research institute in Wako, Japan, found that the energy and width of the tetraneutrons were around 2.4 and 1.8 million electron volts, respectively. Both are larger than the theory results, but Vary said the uncertainties in the current theoretical and experimental results could cover these differences.
“A tetraneutron is so short-lived that it’s such a shock to the world of nuclear physics that its properties can be measured before it breaks down,” Vary said. “It’s a very exotic system.”
It is, in fact, “an entirely new state of matter,” he said. “It’s short-lived, but it points to possibilities. What happens if you put two or three of these together? Could you get more stability?”
Experiments to find a tetraneutron began in 2002, when the structure was proposed in certain reactions involving one of the elements, a metal called beryllium. A team at RIKEN found evidence of a tetraneutron in experimental results published in 2016.
“The tetraneutron will join the neutron as only the second uncharged element of the nuclear graph,” wrote Vary in a project summary. This “provides a valuable new platform for theories of strong interactions between neutrons.”
Meytal Duer of the Institute of Nuclear Physics at the Technical University of Darmstadt is the corresponding author of the Nature article, entitled “Observation of a system of four correlated free neutrons” and announcing the experimental confirmation of a tetraneutron. The results of the experiment are considered a five sigma statistical signal, denoting a definitive finding with a one in 3.5 million chance that the finding is a statistical anomaly.
The theoretical forecast was published on October 28, 2016, in Physical Review Letters, entitled “Prediction for a four-neutron resonance”. Andrey Shirokov of the Skobeltsyn Institute for Nuclear Physics at Moscow State University in Russia, who was a visiting scientist in the State of Iowa, is the first author. Vary is one of the corresponding authors.
“Can we create a small neutron star on Earth?” Vary titled a summary of the tetraneutron project. A neutron star is what’s left when a massive star runs out of fuel and collapses into a superdense neutron structure. The tetraneutron is also a neutron structure, one Vary jokes that it is a “short-lived, very light neutron star”.
Vary’s personal reaction? “I had pretty much given up on the experiments,” he said. “I hadn’t heard anything about this during the pandemic. That was quite a shock. Oh my God, here we are, we might actually have something new.”
Physicists demonstrate the existence of a new subatomic structure
M. Duer et al, Observation of a system of four correlated free neutrons, Nature (2022). DOI: 10.1038/s41586-022-04827-6
Provided by Iowa State University
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