Over the last two years, a Hungarian group of physicists at the Atomki Institute have observed two examples of a mysterious particle, dubbed X17, that hints at a fifth force of nature. An experiment at CERN called NA64 has also been searching for this particle, and now new upgrades may help further probe the existence (or not) of this particle.
In the NA64 experiment, scientists shoot a beam of tens of billions of electrons at a fixed target. The collision between the electrons and the atoms in the target produce particles, potentially those we have never seen before. So far, NA64 has not found any trace of X17, but even no detection is useful. It tells researchers that if the particle does indeed exist, there are certain values for the strength of the interaction between X17 and electrons that can be excluded.
"The Atomki anomalies could be due to an experimental effect, a nuclear physics effect or something completely new such as a new particle. To test the hypothesis that they are caused by a new particle, both a detailed theoretical analysis of the compatibility between the beryllium-8 and the helium-4 results as well as independent experimental confirmation is crucial,” Sergei Gninenko, spokesperson for the NA64 collaboration at CERN, said in a statement.
Even though many consider the existence of the particle unlikely, the two detections have physicists buzzing with excitement. The detection is not predicted in the current theoretical landscape of particle physics, so if it does exist, it can't be interacting through the four established forces of nature: gravity, electromagnetism, and the strong and weak nuclear forces.
“By 2023, the LHCb experiment should be able to make a definitive measurement to confirm or refute the interpretation of the Atomki anomalies as arising from a new fundamental force. In the meantime, experiments such as NA64 can continue to chip away at the possible values for the hypothetical particle’s properties, and every new analysis brings with it the possibility (however remote) of discovery," said Jesse Thaler, a theoretical physicist from the Massachusetts Institute of Technology.
If the discovery is confirmed, it will completely change fundamental physics. X17 and similar hypothetical particles are often referred to as dark photons, and some physicists believe their existence is key to explaining other yet-to-be-confirmed theories, such as dark matter and dark energy.