Tetraneutron Experimental Discovery: An Unusual 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. Vary, a professor of physics and astronomy at Iowa State University, stated, "We constantly have to declare we're waiting for experimental evidence." 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 the 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 might also possess qualities that are advantageous to current or future technological advancements.

You undoubtedly 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, aren't stable and eventually decay into protons. Double and triple neutron combinations also don't create resonances, which are states of matter that are momentarily stable before decomposing. Using the supercomputing power at the Lawrence Berkeley National Laboratory in California, the 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 second. It’s hard to believe, but that’s long enough for physicists to study.

This graph shows experimental measurements and theoretical predictions for the tetraneutron’s energy and width, essential properties of this exotic state of matter. The measurements are in millions of electron volts, a common unit of measurement in high-energy and nuclear physics. The most recent experimental results are second from the left and labelled 2022. The theoretical predictions by the research group that includes Iowa State’s James Vary are the four columns labelled “NCSM” and represent results from different realistic inter-neutron interactions. These results were published in 2016 and 2018. The theoretical predictions labelled “GSM” were published in 2019 by a group based in China. They use a different method that complements the NCSM method. Publication details are also listed. Credit: James Vary/Iowa State University

According to predictions made by physicists, the tetraneutron should possess the energy of around 0.8 million electron volts (a unit of measurement common in high-energy and nuclear physics visible light has energies of about 2 to 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.

The fact that a tetraneutron may have its parameters evaluated before it disintegrates is a very major shock to the nuclear physics community, according to Vary. It's a really unusual system. In actuality, he claimed, it is "a completely new condition of matter." "It's fleeting, but it suggests possibilities. What happens when you combine two or three of these? Would you be able to gain 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. According to Vary's project overview, "the tetraneutron will become just the second chargeless element of the nuclear table, joining the neutron." For theories of the strong interactions between neutrons, this "provides a valuable new platform."

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 possibilities that the finding is a statistical aberration. On October 28, 2016, the journal Physical Review Letters published the theoretical prediction (Prediction for a Four-Neutron Resonance). The first author is Andrey Shirokov, a visiting scientist from the Skobeltsyn Institute of Nuclear Physics at Moscow State University in Russia. One of the corresponding writers is Vary. The theoretical study was funded by grants from the Russian Science Foundation, the German and US Nuclear Theory Exchange Program, the National Energy Research Scientific Computing Center, and the US Department of Energy.

Can we build a tiny neutron star here on Earth? A synopsis of the tetraneutron project may have several titles. When a big star runs out of fuel and collapses into a super-dense neutron structure, a neutron star is what is left. The tetraneutron, which varies quips is a "short-lived, very-light neutron star," is likewise a neutron structure. Vary said, "I had very well given up on the studies." "During the epidemic, I had no knowledge of this. This was a major surprise. Oh my God, perhaps we genuinely have something novel here.