Thanks to neitsnie and causal observer for the link to a CNN article reporting that a research team from the Institute for Nuclear Research at the Hungarian Academy of Sciences (Atomki) led by physicist Attila Krasznahorkay claim to have observed a particle they call X17 which they think could connect our visible world with the world of dark matter. They found the particle when they observed how light emitted from an excited helium split at an angle of 115 degrees, which is not in keeping with the laws of known physics. Previously they had observed electrons and positrons splitting from a beryllium-8 atom at 140 degrees, again unusual according to physics.
These findings are leading some to conclude that there is a fifth force of nature at work (in addition to gravity, electromagnetism, the strong nuclear force and the weak nuclear force.
The CNN article titled “A ‘no-brainer Nobel Prize’: Hungarian scientists may have found a fifth force of nature” is here:
The news article references a paper on Archiv.org titled “New evidence supporting the existence of the hypothetic X17 particle”
We observed electron-positron pairs from the electro-magnetically forbidden M0 transition depopulating the 21.01 MeV 0− state in 4He. A peak was observed in their e+e− angular correlations at 115∘ with 7.2σ significance, and could be described by assuming the creation and subsequent decay of a light particle with mass of mXc2=16.84±0.16(stat)±0.20(syst) MeV and ΓX= 3.9×10−5 eV. According to the mass, it is likely the same X17 particle, which we recently suggested [Phys. Rev. Lett. 116, 052501 (2016)] for describing the anomaly observed in 8Be.