The experiment with four neutrons found evidence of a long-sought particle made up of four neutrons.
While all atomic nuclei except hydrogen are made up of protons and neutrons, physicists have been searching for a particle made up of one, three or four neutrons for more than half a century. Experiments conducted by a team of physicists from the Technical University of Munich (TUM) in the accelerator lab at the Garching research campus indicate that a particle with four bound neutrons may be present.
While nuclear physicists agree that there are no proton-only systems in the universe, they have been searching for particles made up of one, three, or four neutrons for more than 50 years.
At the Van de Graaff tandem accelerator at the Maier-Leibnitz laboratory on the Garching Research Campus, a team of physicists from the Technical University of Munich (TUM) bombarded a lithium-7 target with a lithium-7 atomic nucleus accelerated to 12 percent of the speed of light. All measurement results indicate that their experiments yielded the desired carbon-10 and tetraneutron. Credit: Sonja Battenberg/TUM
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If such a particle exists, parts of the strong interaction theory must be reconsidered. In addition, studying these particles more closely can help us better understand the properties of neutron stars.
“A strong interaction is literally the force that holds the world at its core. Atoms heavier than hydrogen would be unthinkable without it,” said Dr Thomas Westermann, who led the experiments.
Everything now points to the fact that it is precisely these kinds of particles that arose in one of the recent experiments conducted on Van de Graaf’s now-defunct tandem particle accelerator at the Garching research campus.
At the Van de Graaff tandem accelerator at the Maier-Leibnitz laboratory on the Garching research campus, a team of physicists from the Technical University of Munich (TUM) bombarded a lithium-7 target with a lithium-7 atomic nucleus, accelerating to 12. percent the speed of light. All measurement results indicate that their experiments yielded the desired carbon-10 and tetraneutron. Credit: Thomas Faestermann/TUM
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The long search for a tetraneutron
Twenty years ago, a French research group published measurements that they interpreted as a signature of the desired tetraneutron. However, later work by other groups showed that the method used could not prove the existence of a tetraneutron.
In 2016, a group in Japan attempted to make a tetraneutron from helium-4 by bombarding it with a beam of radioactive helium-8 particles. This reaction should produce beryllium-8. In fact, they were able to detect four such atoms. From the measurement results, the researchers concluded that the tetraneutron was uncorrelated and rapidly fell back into four neutrons.
dr. Thomas Westermann at the Van de Graaff tandem accelerator access hatch on the Garching research campus. Here, more than ten million volts of lithium ions accelerated to about 12 percent of the speed of light. Westermann and his team fired on a lithium-7 target with these lithium ions. All measurement results indicate that their experiments yielded the desired carbon-10 and tetraneutron. Credit: Ole Benz/TUM
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In their experiments, Westermann and his team bombarded a lithium-7 target with lithium-7 particles that accelerated to about 12 percent of the speed of light. In addition to the tetraneutron, it should produce carbon-10. Indeed, physicists have managed to discover this species. Repetition confirmed the result.
circumstantial evidence
The team’s measurements matched the expected signature of carbon 10 in its first excited state and a bound tetraneutron of 0.42 megaelectronvolts (MeV). According to the measurements, the tetraneutron will be about as stable as the neutron itself. It then decays through beta decay with a half-life of 450 seconds. “For us, this is in all respects the only reasonable physical explanation for the measured values,” explains Dr Thomas Westermann.
dr. Roman Gernhäuser, a researcher in the Department of Physics at the Technical University of Munich (TUM), is in the target chamber of the Van de Graaff tandem accelerator on the Garching campus, where lithium ions accelerated to about 12 percent the speed of light, the purpose of lithium 7. All measurement results indicate that their experiments produced the desired carbon-10 and tetraneutron. Credit: Ole Benz/TUM
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From their measurements, the team achieved a certainty of more than 99.7 percent or 3 sigma. But in physics, the existence of the particle is not considered definitive until the certainty of 5 sigma is reached. Therefore, researchers are now eagerly awaiting independent confirmation.
Reference: “Indicators for a Coupled Quaternary Neutron” By Thomas Westermann, Andreas Bergmayer, Roman Gernhauser, Dominic Kohl, and Mahmoud Mahgoub, 26 Nov. 2021 Available here. Physics Letters B.
DOI: 10.1016 / j.physletb.2021.136799
The Mayer-Leibnitz laboratory, with its Van de Graaf tandem accelerator, is jointly operated by the Technical University of Munich and the Ludwig Maximilian University of Munich. The facility was closed in early 2020 for structural reasons. All five authors of the publication are graduates or employees of the Technical University of Munich.
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