The four-neutron experiment found evidence of the long-sought particle consisting of four neutrons.
While all atomic nuclei except hydrogen are composed of protons and neutrons, physicists have been searching for particles consisting of one, three, or four neutrons for more than half a century. Experiments carried out by a team of physicists from the Technical University of Munich (TUM) in the accelerator laboratory at the Garching research campus suggest that particles with four bound neutrons may exist.
While nuclear physicists agree that there is no system in the universe made of only protons, they have been searching for particles consisting of one, three, or four neutrons for more than 50 years.
On the Van de Graaff tandem accelerator of the Maier-Leibnitz Laboratory at the Garching Research Campus, a team of physicists from the Technical University of Munich (TUM) bombarded a lithium-7 target with lithium-7 atomic nuclei that had been accelerated to 12 percent the speed of light. All measurements show that their experiments yielded the desired carbon-10 and tetraneutrons. Credit: Sonja Battenberg / TUM
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If such a particle exists, this part of the strong interaction theory will have to be rethought. In addition, studying these particles in greater detail can help us better understand the properties of neutron stars.
“Strong interaction is literally the force that holds the world at its core. Atoms heavier than hydrogen cannot be imagined without them,” said Dr. Thomas Westermann, who directed the experiment.
Everything now points to the fact that exactly this type of particle was created in one of the recent experiments carried out at the now-defunct Van de Graaf tandem particle accelerator at the Garching research campus.
At the Van de Graaff tandem accelerator of 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 lithium-7 atomic nuclei, accelerating to 12 percent. speed of light. All measurements show that their experiments yielded the desired carbon-10 and tetraneutrons. Credit: Thomas Faestermann / TUM
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Long search for tetraneutron
Twenty years ago, a French research group published measurements they interpreted as the signature of the desired tetraneutron. However, subsequent work by other groups showed that the methodology used could not prove the existence of tetraneutrons.
In 2016, a group in Japan attempted to produce tetraneutrons from helium-4 by bombarding them with beams of radioactive helium-8 particles. This reaction should yield beryllium-8. In fact, they were able to detect four such atoms. From the measurement results, the researchers concluded that the tetraneutrons were uncorrelated and rapidly decayed back to four neutrons.
Dr. Thomas Westermann at the Van de Graaff tandem accelerator access door at the Garching research campus. Here, more than ten million volts accelerate lithium ions to about 12 percent the speed of light. Westermann and his team bombarded lithium-7 targets with these lithium ions. All measurements show that their experiments yielded the desired carbon-10 and tetraneutrons. Credit: Ole Benz / TUM
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In their experiment, Westermann and his team bombarded a lithium-7 target with lithium-7 particles that accelerated to about 12 percent the speed of light. In addition to the tetraneutron, it must produce carbon-10. Indeed, physicists have managed to find this species. Repetition confirms the result.
indirect evidence
The team’s measurement results match the expected signature of carbon 10 in the first excited state and a 0.42 megaelectronvolt (MeV) bonded tetraneutron. According to measurements, the tetraneutron will be more or less stable as the neutron itself. It then decays by beta decay with a half-life of 450 seconds. “To us, this is the only plausible physical explanation for the measurable values in all respects,” explains Dr. Thomas Westermann.
Roman Gernhäuser, a researcher in the Department of Physics at the Technical University of Munich (TUM), is in the target room of the Van de Graaff tandem accelerator on the Garching campus, where lithium ions are accelerated to about 12 percent the speed of light, hitting a lithium 7 target. that their experiment yielded the desired carbon-10 and tetraneutrons. Credit: Ole Benz / TUM
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From their measurements, the team achieved more than 99.7 percent certainty, or 3 sigma. But in physics, the existence of a particle is only considered conclusive after 5 sigma certainty is reached. As such, the researchers are now awaiting independent confirmation.
Reference: “Indicators for Linked Quaternary Neutrons” by Thomas Westermann, Andreas Bergmayer, Roman Gernhauser, Dominic Kohl, and Mahmoud Mahgoub, 26 November 2021 Available here. Physics Letter 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 for structural reasons in early 2020. The five authors of this publication are graduates or employees of the Technical University of Munich.
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