Experimental Discovery of a Tetraneutron – An Exotic State of Matter

James Vary, a theoretical physicist, and his colleagues first proposed, predicted, and announced the existence of a "tetraneutron" in a presentation in the summer of 2014, followed by a research paper in the fall of 2016. Since then, they have been waiting for nuclear physics experiments to confirm their findings.

“Whenever we present a theory, we always have to say we’re waiting for experimental confirmation,” stated Vary, an Iowa State University professor of physics and astronomy.

That day has come for Vary and a global team of physicists in the case of four neutrons (very, very briefly) bonded together in a transient quantum state or resonance.

An international team led by researchers from Germany's Technical University of Darmstadt has just reported the experimental finding of a tetraneutron. This discovery opens up new avenues for investigation and may help us comprehend how the cosmos came to be. This novel and unusual state of matter could also possess qualities that are advantageous to current or future technological advancements.

First, how about a definition

You may recall from physics class that protons and neutrons, which are subatomic particles with positive charges, unite to form the atomic nucleus of an atom. Individual neutrons, however, are not stable and eventually decay into protons. Additionally, combinations of double and triple neutrons don't create a resonance, a state of matter that is momentarily stable before it decays.

Enter the tetraneutron

The theorists estimated that four neutrons might produce a resonant state with a lifespan of just 310(-22) seconds, or less than a billionth of a billionth of a second, using the supercomputing capability of the Lawrence Berkeley National Laboratory in California. That's long enough for physicists to study, which is hard to believe.

A detail or two

According to the theorists' predictions, the energy of the tetraneutron should be around 0.8 million electron volts (an electron volt is a unit of measurement used in high-energy and nuclear physics; the energy of visible light is between 2 and 3 electron volts). The calculations also indicated that the diameter of the displayed tetraneutron energy spike would be around 1.4 million electron volts. The researchers then released analyses that showed the breadth would be between 1.1 and 1.7 million electron volts and the energy would most likely be between 0.7 and 1.0 million electron volts. The adoption of several potential possibilities for the interaction between the neutrons led to this sensitivity.

Tetraneutron energy and breadth were discovered to be around 2.4 and 1.8 million electron volts, respectively, in studies at the Radioactive Isotope Beam Factory at the RIKEN research center in Wako, Japan, according to a recently published publication in the journal Nature. Both of these are greater than the theoretical values, although Vary said that uncertainties in the most recent theoretical and experimental findings may account for these discrepancies.

Why it’s a big deal

“A tetraneutron has such a short life it’s a pretty big shock to the nuclear physics world that its properties can be measured before it breaks up,” according to Vary. “It’s a very exotic system.”

He said that it actually represents “a whole new state of matter”. “It’s short-lived, but points to possibilities. What happens if you put two or three of these together? Could you get more stability?”

When the structure was suggested in specific interactions involving one of the elements, a metal called beryllium, searches for a tetraneutron began in 2002. In experimental findings released in 2016 by a team at RIKEN, tetraneutron hints were discovered.

“The tetraneutron will join the neutron as only the second chargeless element of the nuclear chart,” Vary stated in a project overview. That “provides a valuable new platform for theories of the strong interactions between neutrons.” 

The papers, please

The Nature study titled "Observation of a correlated free four-neutron system" reporting the experimental confirmation of a tetraneutron is co-authored by Meytal Duer of the Institute for Nuclear Physics at the Technical University of Darmstadt. The results of the experiment are regarded as a five-sigma statistical signal, indicating a conclusive discovery with a one in 3.5 million possibility that the finding is a statistical aberration.

Physical Review Letters published the theoretical forecast on October 28, 2016. (Prediction for a Four-Neutron Resonance). First author is visiting scientist at Iowa State from the Skobeltsyn Institute of Nuclear Physics at Moscow State University in Russia, Andrey Shirokov. One of the authors who corresponds is Vary. The theoretical study was funded by grants from the German and American Nuclear Theory Exchange Program, the Russian Science Foundation, the National Energy Research Scientific Computing Center, and the US Department of Energy.

Written with a smile

“Can we create a small neutron star on Earth?” The tetraneutron project overview has several titles. When a large star runs out of fuel and collapses into a highly dense neutron structure, what is left is a neutron star. According to Vary, the tetraneutron is a "short-lived, very-light neutron star" and is also a neutron structure.

A personal reaction

“I had pretty much given up on the experiments,” Vary stated. “I had heard nothing about this during the pandemic. This came as a big shock. Oh my God, here we are, we may actually have something new.”

Reference: “Observation of a correlated free four-neutron system” by M. Duer, T. Aumann, R. Gernhäuser, V. Panin, S. Paschalis, D. M. Rossi, N. L. Achouri, D. Ahn, H. Baba, C. A. Bertulani, M. Böhmer, K. Boretzky, C. Caesar, N. Chiga, A. Corsi, D. Cortina-Gil, C. A. Douma, F. Dufter, Z. Elekes, J. Feng, B. Fernández-Domínguez, U. Forsberg, N. Fukuda, I. Gasparic, Z. Ge, J. M. Gheller, J. Gibelin, A. Gillibert, K. I. Hahn, Z. Halász, M. N. Harakeh, A. Hirayama, M. Holl, N. Inabe, T. Isobe, J. Kahlbow, N. Kalantar-Nayestanaki, D. Kim, S. Kim, T. Kobayashi, Y. Kondo, D. Körper, P. Koseoglou, Y. Kubota, I. Kuti, P. J. Li, C. Lehr, S. Lindberg, Y. Liu, F. M. Marqués, S. Masuoka, M. Matsumoto, J. Mayer, K. Miki, B. Monteagudo, T. Nakamura, T. Nilsson, A. Obertelli, N. A. Orr, H. Otsu, S. Y. Park, M. Parlog, P. M. Potlog, S. Reichert, A. Revel, A. T. Saito, M. Sasano, H. Scheit, F. Schindler, S. Shimoura, H. Simon, L. Stuhl, H. Suzuki, D. Symochko, H. Takeda, J. Tanaka, Y. Togano, T. Tomai, H. T. Törnqvist, J. Tscheuschner, T. Uesaka, V. Wagner, H. Yamada, B. Yang, L. Yang, Z. H. Yang, M. Yasuda, K. Yoneda, L. Zanetti, J. Zenihiro and M. V. Zhukov, 22 June 2022, Nature.

DOI: 10.1038/s41586-022-04827-6

Experimental Discovery of a Tetraneutron – An Exotic State of Matter Experimental Discovery of a Tetraneutron – An Exotic State of Matter Reviewed by Lilit on June 27, 2022 Rating: 5
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