With the emergence of a new mysterious particle, X17, scientists think they are taking another step towards the discovery of a fifth force of nature.
How do objects interact with each other? What rules govern the elements of our Universe, even at the other end of space? For our human brains, this reality remains difficult to understand and visualise. To simplify it, scientists have invented the notion of 'forces of nature.' These make it possible to describe and predict all the phenomena that surround us.
There are four fundamental forces. First of all, gravitation is responsible for the attraction of bodies. This is what allows us to keep our feet on the ground, for example. Electromagnetism makes it possible to bind atoms together to form molecules, the basis of matter. Finally, nuclear interactions (strong interaction and weak interaction) ensure the cohesion of atomic nuclei.
But there are still deficiencies in this standard model. Some events still cannot be physically explained. These four elementary interactions are no longer enough. Many statements, so far lacking foundation, have therefore been made regarding the existence of a fifth force. But the hunt for dark matter, this invisible theoretical substance supposed to represent about 80% of the mass of the Universe, remains particularly unsuccessful.
A discovery far from the standard model
Scientists at the Atomki Nuclear Research Institute (Hungary) believe they have found new, stronger evidence. By 2015, they had already reported some surprising results. They were then studying the light emitted during the disintegration of an unstable atom, beryllium-8. Studies around this chemical element are aimed at understanding how nuclear fusion in stars forms new elements. They were then looking for potential 'dark photons,' which were suggested as the main support for dark matter. But that's not what they found.
They found that this disintegration of beryllium-8 did not produce the expected light emissions. The standard model is that when the atom disintegrates, electron pairs and their opposites, positrons - two of the components of the atom that separate when the atom is destroyed - decrease. Instead, they observed that they were moving away from each other at a particular angle while multiplying - thus forming a small 'tremor.'
The X17 boson
And if several experts were sceptical at the time about this phenomenon, it does not seem to be a coincidence: the new research from 2019 reported the same observation, this time with an isotope of helium, with characteristics similar to those of beryllium-8. The results are made available in an article, pending their acceptance in a journal.
What does that mean, then? Researchers believe that as soon as the atom disintegrates, the excess energy between its parts briefly creates an unknown new particle. It would then be destroyed almost immediately, forming a pair of electrons and positions. It was named X17, because its mass would be about 17 Mev or 34 times that of an electron. It is finally described as a 'photophobic X-boson' - the bosons being particles that can carry forces. The action of X17 would act over macroscopic distances, not much larger than those of the nucleus of an atom.
If new research eventually validates the existence of the particle, physicists will have to re-evaluate all interactions between the four fundamental forces, in order to make way for a fifth. 'We expect further independent experimental results for particle X17 in the coming years,' concluded the research team.