Checking the $^8$Be anomaly with a two-arm electron positron pair spectrometer

TL;DR

This study replicates a previous experiment suggesting a potential new particle, confirming the anomaly at one resonance energy while refuting it at others, using a different spectrometer setup for validation.

Contribution

It provides an independent verification of the $^8$Be anomaly with a different spectrometer, strengthening the evidence for the potential new particle X17.

Findings

Confirmed the anomaly at E_x=18.15 MeV resonance.

Did not observe the anomaly at E_x=17.6 MeV resonance.

No anomaly detected at E_p=800 keV off resonance energies.

Abstract

We have repeated the experiment performed recently by Krasznahorkay et al., (Phys. Rev. Lett. 116, 042501 (2016)), which may indicate a new particle called X17 in the literature. In order to get a reliable, and independent result, we used a different type of electron-positron pair spectrometer which have a more simple acceptance/efficiency as a function of the correlation angle, but the other conditions of the experiment were very similar to the published ones. We could confirm the presence of the anomaly measured at the E$_x$=18.15 MeV resonance, and also confirm their absence at the E$_x$=17.6 MeV resonance, and at E$_p$= 800 keV off resonance energies.