Observation of Anomalous Internal Pair Creation in $^8$Be: A Possible Signature of a Light, Neutral Boson

TL;DR

The paper reports an anomalous electron-positron pair creation in beryllium-8 that could suggest the existence of a new light, neutral boson with specific mass and quantum numbers.

Contribution

It presents experimental evidence of an unexpected internal pair creation anomaly in $^{8}$Be, hinting at a possible new light, neutral boson not accounted for in current physics models.

Findings

Significant deviation from expected pair creation at large angles.

Potential indication of a new neutral boson with mass 16.70 MeV/c^2.

Observation with confidence level > 5 sigma.

Abstract

Electron-positron angular correlations were measured for the isovector magnetic dipole 17.6 MeV state ($J^\pi=1^+$, $T=1$) $\rightarrow$ ground state ($J^\pi=0^+$, $T=0$) and the isoscalar magnetic dipole 18.15 MeV ($J^\pi=1^+$, $T=0$) state $\rightarrow$ ground state transitions in $^{8}$Be. Significant deviation from the internal pair creation was observed at large angles in the angular correlation for the isoscalar transition with a confidence level of $> 5\sigma$. This observation might indicate that, in an intermediate step, a neutral isoscalar particle with a mass of 16.70$\pm0.35 $ (stat)$\pm 0.5 $ (sys) MeV$/c^2$ and $J^\pi = 1^+$ was created.