What is X17 particle?

The X17 particle is a hypothetical particle that has been proposed in the context of certain theoretical frameworks in particle physics, particularly involving dark matter and beyond the Standard Model physics. The particle gained attention due to research suggesting the possible existence of a particle with a mass around 17 MeV/c² (mega-electronvolts per speed of light squared) exhibiting unusual properties. The interest in the X17 particle primarily stems from an experiment conducted by researchers at the Hungarian Academy of Sciences, who reported observations that could indicate the existence of this particle based on anomalies in the decay of certain isotopes. The findings hinted at a new force or a mediator of interactions beyond those described by the Standard Model, potentially providing insights into dark matter, which constitutes a significant portion of the universe's mass-energy content but has yet to be directly detected. As of my last knowledge update in October 2023, the X17 particle remains a theoretical proposition, and further experimental evidence is needed to confirm its existence. Research into such particles is ongoing and is part of a broader effort to explore phenomena that could help address unresolved questions in particle physics and cosmology.