The tetra-neutron - experiment finds evidence for a long-sought particle comprising four neutrons
Understanding of nuclear forces might have to be significantly changed


Date:
December 10, 2021
Source:
Technical University of Munich (TUM)
Summary:
While all atomic nuclei except hydrogen are composed of protons and
neutrons, physicists have been searching for a particle consisting
of two, three or four neutrons for over half a century. Experiments
by a team of physicists now indicate that a particle comprising
four bound neutrons may well exist.



FULL STORY ========================================================================== While all atomic nuclei except hydrogen are composed of protons and
neutrons, physicists have been searching for a particle consisting of
two, three or four neutrons for over half a century. Experiments by a
team of physicists of the Technical University of Munich (TUM) at the accelerator laboratory on the Garching research campus now indicate that
a particle comprising four bound neutrons may well exist.


========================================================================== While nuclear physicists agree that there are no systems in the universe
made of only protons, they have been searching for particles comprising
two, three or four neutrons for more than 50 years.

Should such a particle exist, parts of the theory of the strong
interaction would need to be rethought. In addition, studying these
particles in more detail could help us better understand the properties
of neutron stars.

"The strong interaction is literally the force that holds the world
together at its core. Atoms heavier than hydrogen would be unthinkable
without it," says Dr. Thomas Faestermann, who directed the experiments.

Everything now points to the fact that precisely these kinds of
particles were created in one of the last experiments carried out at
the now decommissioned tandem Van de Graaff particle accelerator on the Garching research campus.

The long search for the tetra-neutron As early as 20 years ago, a
French research group published measurements that they interpreted as
the signature of the sought-after tetra-neutron. However, later work
by other groups showed that the methodology used could not prove the
existence of a tetra-neutron.

In 2016, a group in Japan attempted to produce tetra-neutrons
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 their measurement results, the researchers concluded that the tetra- neutron was unbound and quickly decayed back into four neutrons.

In their experiments, Faestermann and his team bombarded a lithium-7
target with lithium-7 particles accelerated to about 12 percent of the
speed of light.

In addition to the tetra-neutron, this should produce carbon-10. And
indeed, the physicists succeeded in detecting this species. A repetition confirmed the result.

Circumstantial evidence The team's measurement results matched the
signature that would be expected from carbon-10 in its first excited state
and a tetra-neutron bound by 0.42 megaelectronvolts (MeV). According to
the measurements the tetra-neutron would be roughly as stable as the
neutron itself. It would then decay by beta-decay with a half-life of
450 seconds. "For us, this is the only physically plausible explanation
of the measured values in all respects," explains Dr. Thomas Faestermann.

With their measurements, the team achieves a certainty of well over
99.7 percent, or 3 sigma. But in physics, the existence a particle
is only considered conclusively proven once a certainty of 5 sigma is
achieved. Thus, the researchers are now eagerly awaiting independent confirmation.

========================================================================== Story Source: Materials provided by
Technical_University_of_Munich_(TUM). Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Thomas Faestermann, Andreas Bergmaier, Roman Gernha"user,
Dominik Koll,
Mahmoud Mahgoub. Indications for a bound tetraneutron. Physics
Letters B, 2022; 824: 136799 DOI: 10.1016/j.physletb.2021.136799 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211210103103.htm

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