MEG II PRESENTS ITS FIRST RESULT IN THE SEARCH FOR A NEW BOSON, the X17
The results, presented by prof. Gianluca Cavoto (Sapienza University of Rome and INFN affiliate), are detailed in an article published on arXiv and submitted to the European Journal of Physics C. The results just presented do not show evidence of the sought particle.
The MEG II experiment, which is currently collecting data at the PSI laboratory, investigates new physics phenomena and is designed specifically to search for the decay of a positive muon into a positron and a photon.
The MEG II detector is also capable of studying other phenomena, such as the production of this new particle, X17.
The observation of an anomalous structure in the opening angle distribution of electron-positron pairs produced in a proton-induced nuclear reaction on a lithium target was reported by an experiment at the ATOMKI laboratory (Debrecen, Hungary) and interpreted as the production and subsequent decay of a hypothetical particle, named X17 due to its mass (17 MeV). Similar excesses, consistent with this particle, were later observed in processes involving helium and carbon nuclei using the same experimental technique.
The MEG II apparatus uses protons from a Cockroft-Walton accelerator with energy up to 1.1 MeV impacting a lithium target. The electron-positron pair emerging from the lithium-to-beryllium nuclear transition was studied with various detectors, including a spectrometer (a gaseous detector in a magnetic field) with a broader angular acceptance than previous experiments. No significant signal was found, and 90% confidence level (C.L.) limits were set on the X17 production rate relative to photon emission at the two beryllium resonances explored in the experiment, characterized by energies of 17.6 MeV and 18.1 MeV, respectively. The ATOMKI result is compatible with these observations with a p-value of 6%.
The MEG II collaboration brings together over 50 physicists from research institutions in Italy, Japan, Russia, Switzerland, and the United States, including INFN. A joint INFN Roma and Sapienza group (G.Cavoto, D. Pasciuto, V. Pettinacci, F.Renga, C.Voena) is part of this collaboration since many years working and had a key role in the proposal, design, realization and data analysis of this measurement.
Magazine: European Journal of Physics C
Article : https://arxiv.org/abs/2411.07994