X17 particle: evidence for fifth force of nature greatly increased

A new confirmation by a Hungarian team of the existence of an as yet unknown boson, this time in the decay of helium, suggests that we are on the trail of an as yet unknown particle - and thus one that does not appear in the Standard Model. If this experiment is reproduced.

Missing impulse
In 2016, the team measured the decline of an excited beryllium-8 core. Excited nuclei are at a higher energy level than nuclei in the ground state. Over time, they bounce back into the ground state, emitting the extra energy in the form of a particle, usually a photon or particle pair. This is a well-known process in atomic physics. We also know how atomic nuclei behave in this case. Under the iron law of conservation of momentum, all emitted particles must have an added momentum of zero. For example, if a particle deflects to the right at an angle of 15 degrees, an equally heavy particle must deflect 15 degrees to the left, or, for example, a half as heavy particle 30 degrees to the left. If this sum is no longer correct, there must be a missing particle. The neutrino was also discovered in this way eighty years ago. During the radioactive decay of atomic nuclei, the researchers discovered that a small amount of impulse was missing. This impulse turned out to belong to a still unknown particle, which we now know is the neutrino.

A fifth force of nature can possibly explain dark matter and / or dark energy. Source: NASA

This is roughly what the researchers observed with the beryllium nuclei. These fell back to the ground state, when an unknown particle was emitted. This particle disintegrated into an electron positron pair in a short time. The experiment was repeated in the years that followed, this time with a helium-4 core. Here, too, an unknown particle with a comparable mass appeared to be released. Based on this, the team suspects that it is the same particle, that they have christened the 'X17 boson'.

We know from the X17 particle that it disintegrates into an electron positron pair and is about 35 times as heavy as the electron, a little below 17 MeV / c². Hence the provisional name. The particle only reacts with neutrons, not with protons, because it would be 'proton-phobic' [3]. This behavior is the opposite of that of photons, which respond to protons (and electrons) but not to the electrically neutral neutrons. This would also explain why this particle has not been discovered so far.

No physicist has yet succeeded in finding an explanation for X17 within the standard model. That would mean that we have observed for the first time a particle that does not fit within the Standard Model - and thus opens the gate to new physics and a fifth force of nature.

How certain are these discoveries?
The measurement accuracy is great. The chance that these results are coincidental is 7.1 sigma, in other words less than 1 in the 400 billion [2]. This, combined with the earlier experiment, means that we can conclude - based on the work of this group - that these measurements are valid and that a new, unknown phenomenon has actually been observed, which up to now cannot be explained with the known Standard Model. . It cannot be ruled out that we will miss a statement, although this chance is small. With a fairly high probability, this is therefore 'new physics'. Finally. And that's beyond the massive LHC experiment, which has only demonstrated the existence of the Higgs boson.

There are, however, some doubts within the physics community about these observations, especially because this group has previously made similar claims, which had to withdraw them by using more accurate measuring equipment [4]. Hopefully there will be an experiment from another group soon, confirming these observations.

What are the consequences?
Just as the behavior of a billiard ball can easily be described with Newtonian high school physics and it is not necessary to let go of relativity theory, this discovery will have few consequences in daily life. Short-term. As soon as we succeed in drawing up equations for this new force of nature, this opens up unprecedented possibilities. We may be able to uncover the riddles of dark matter and dark energy through the new physics. Should we succeed in this, and learn to use both natural phenomena, then the universe would be open to us and possibly even grow into Kardashev-IV civilization. Possibly the consequences will remain limited, such as with the discovery of the neutrino, which we can still do very little with.

1. Presentation 8Be anomaly, CNNP, Catania, 2017
2. AJ Krasznahorkay, M. Csatlós, L. Csige, J. Gulyás, M. Koszta, B. Szihalmi and J. Timár, New evidence supporting the existence of the hypothetic X17 particle, ArXiv preprint server, 2019 (submitted for Physical Review Letters)
3. Jonathan L. Feng, Bartosz Fornal, Iftah Galon, Susan Gardner, Jordan Smolinsky, Tim MP Tait, Philip Tanedo,  Protophobic Fifth Force Interpretation of the Observed Anomaly in 8Be Nuclear Transitions, ArXiv preprint server, 2016 (published in Prl)
4. Evidence of a 'Fifth Force' Faces Scrutiny, Quanta Magazine, 2016

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