Speaker
Description
A resonant structure has been observed at ATOMKI in the invariant mass of electron-positron pairs, produced after excitation of nuclei such as $^8$Be and $^4$He by means of proton beams. Such a resonant structure can be interpreted as the production of an hypothetical particle (X17) whose mass is around 17 MeV.
The MEG-II experiment at the Paul Scherrer Institut whose primary physics goal is the search for the charged lepton violation process $\mu$ $\rightarrow$ $ e \gamma$ is in the position to confirm and study this observation. MEG-II employs a source of protons able to accelerate them up to a kinetic energy of about 1 MeV. These protons are absorbed on a thin target where they excite nuclear transitions to produce photons for the Xenon calorimeter calibration of the MEG-II detector
By using a dedicated 2 $\mu$m thick target containing lithium atoms the $^7$Li(p,e$^+$e$^{-}$)$^8$Be process is being studied with a magnetic spectrometer including a cylindrical drift chamber and a system of fast scintillators. This aims to reach a better invariant mass resolution than previous experiments and to study the production of the X17 with a larger acceptance and therefore to shed more light into the nature of this observation.
After a 2022 engineering run, a month-long data-taking was conducted in Feb 2023. We report about our first results on the search and the study of this hypothetical X17 particle.
| Collaboration / Activity | MEG II collaboration |
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