Observation of the X17 anomaly in the $^7$Li($p$,$e^+e^-$)$^8$Be direct proton-capture reaction

TL;DR

This study investigates electron-positron pair emissions in a lithium nuclear reaction, revealing anomalies at certain energies that support the hypothesis of a new particle, X17, being produced and decaying.

Contribution

It provides experimental evidence of anomalies in $e^+e^-$ angular correlations during direct proton capture, supporting the existence of the X17 particle.

Findings

Anomalies observed in off-resonance $e^+e^-$ angular correlations.

Support for the X17 particle hypothesis.

Consistent internal pair creation at resonance energies.

Abstract

Angular correlation spectra of $e^+e^-$ pairs produced in the $^{7}$Li($p$,$\gamma$)$^{8}$Be nuclear reaction have been studied at the sharp $E_p$= 441 keV resonance as well as at $E_p$= 650 keV, 800 keV and 1100 keV proton beam energies. The spectra measured at the resonance can be understood through the M1 internal pair creation process, but in the case of the off-resonance regions (direct proton capture) significant anomalies were observed in the $e^+e^-$ angular correlations supporting the X17 hypothetical particle creation and decay.