One more step towards the observation of the tetraneutron

The target proton ejects an alpha particle (4He) from the 8He projectile nucleus, leaving the remaining 4 neutrons unperturbed in a highly correlated resonant state. A resonance structure compatible with a quasi-bound tetraneutron has indeed been observed in a very clear way, after decades of experimental quest. The energy of the tetraneutron has been reconstructed by an energy balance of the reaction, with the so-called missing mass method, by measuring the energy of the proton and of the alpha particle.

Improving the modeling of nuclear systems

Some theoretical studies where the nuclear interaction is treated in a more or less phenomenological way have shown that a resonant tetraneutron could exist, with a very short lifetime. However, other more microscopic approaches called ab-initio, i.e. formalized from the elementary interaction between neutrons, do not predict such a resonance. This experimental result represents an important challenge: if it turns out that it is not possible to explain otherwise (than by the existence of a resonant tetraneutron) the strong correlation observed recently, the way of constructing the nuclear interaction in ab-initio approaches should probably be revisited and formalized in a slightly different framework.

This result represents an important step that will allow, among other things, to test the way nuclear physicists describe the interaction between nucleons and consequently to improve the modeling of nuclear systems, not only nuclei, but also infinite nuclear matter, an infinite ideal system composed of nucleons whose study helps to understand the properties of nuclei and neutron stars.