James Vary waited for nuclear physics experiments to confirm the reality of a “tetraneutron” that he and his colleagues first theorized, predicted and announced in a summer 2014 presentation, followed by a paper research in the fall of 2016.
“Whenever we present a theory, we always have to say that we are waiting for experimental confirmation,” said Vary, professor of physics and astronomy at Iowa State University.
In the case of four neutrons (very, very) briefly bound together in a temporary quantum state or resonance, that day for Vary and an international team of theorists has now arrived.
The just-announced experimental discovery of a tetraneutron by an international group led by researchers at the German Technical University of Darmstadt opens doors for further research and could lead to a better understanding of how the universe is assembled. This new and exotic state of matter could also have useful properties in existing or emerging technologies.
Neutrons, which you probably remember from science class, are chargeless 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 turn into protons. Nor do combinations of double and triple neutrons form what physicists call a resonance, a state of matter that is temporarily stable before decaying.
Enter the tetraneutron. Using supercomputing power from 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 long enough for physicists to study.
Theorists’ calculations indicate that the tetraneutron should 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.) Calculations also indicated the width of the energy peak plotted showing a tetraneutron would be about 1.4 million electron-volts. Theorists published later studies indicating that the energy would probably 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.
An article that has just appeared in the journal Nature reports that experiments at the RIKEN Research Institute’s Radioactive Isotope Beam Factory in Wako, Japan, revealed that the energy and width of tetraneutrons were about 2.4 and 1.8, respectively. million electron volts. These are both more important than the theoretical results, but Vary said uncertainties in the current theoretical and experimental results could cover these differences.
“A tetraneutron has such a short lifespan that it’s a big enough shock to the world of nuclear physics that its properties can be measured before it shatters,” Vary said. “It’s a very exotic system.”
It is, in fact, “a whole new state of matter,” he said. “It’s short-lived, but it indicates possibilities. What happens if you combine two or three? Could you get more stability?”
Experiments to find a tetraneutron began in 2002 when the structure was proposed in some reactions involving one of the elements, a metal called beryllium. A RIKEN team found hints of a tetraneutron in experimental results published in 2016.
“The tetraneutron will join the neutron as the second chargeless element of the nuclear map,” Vary wrote in a project summary. This “provides a valuable new platform for theories of strong neutron interactions”.
Meytal Duer of the Institute for Nuclear Physics of the Technical University of Darmstadt is the corresponding author of the Nature paper, entitled “Observation of a system with four correlated free neutrons” and announcing the experimental confirmation of a tetraneutron. The results of the experiment are considered a five sigma statistical signal, indicating a definite finding with a one in 3.5 million chance that the finding is a statistical anomaly.
The theoretical prediction was published on October 28, 2016 in Physical examination letters, entitled “Prediction of a four-neutron resonance”. Andrey Shirokov of the Skobeltsyn Institute for Nuclear Physics at Moscow State University in Russia, who was a visiting scholar at Iowa State, 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 remains when a massive star runs out of fuel and collapses into a super-dense neutron structure. The tetraneutron is also a neutron structure, a Vary jokingly being a “short-lived and 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 it during the pandemic. It was a big shock. Oh my God, here we are, we may actually have something new.”
Physicists demonstrate the existence of a new subatomic structure
M. Duer et al, Observation of a system with four correlated free neutrons, Nature (2022). DOI: 10.1038/s41586-022-04827-6
Provided by Iowa State University
Quote: Theoretical calculations predicted the now confirmed tetraneutron, an exotic state of matter (2022, June 22) Retrieved June 23, 2022 from https://phys.org/news/2022-06-theoretical-now-confirmed-tetraneutron -exotic-state.html
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