Abstract
A few years ago we observed anomalous electron-positron angular correlations for the 18.15 MeV M1 transition of 8Be. This was interpreted as the creation and decay of an intermediate bosonic particle with a mass of m 0 c 2=16.70±0.35(stat )±0.5(sys) MeV, which is now called X17. The possible relation of the X17 boson to the dark matter problem triggered an enormous interest in the wider physics community. We also observed a similar anomaly in 4He, which could be described also by the creation and subsequent decay of the same X17 particle. Very recently, the 11B proton capture reaction was used for exciting the 17.2 MeV broad (Γ=1.15 MeV) resonance in 12C and studying their internal pair creation decay. Anomalies were observed in the angular correlation of the electron-positron pairs, which together with the 8Be and 4He data provides kinematic evidence for the X17 particle and supports their vector boson and fifth force explanation.
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