Field not found.

In search of new physics: MEG II updates its record

23 April 2025

The MEG II experiment’s scientific collaboration, which includes the participation of INFN, is presenting a new result today, April 23, 2025, during a seminar at the Paul Scherrer Institute (PSI) in Switzerland.

“This is an important step forward in the search for the decay of a positive muon into a positron and a photon which, if observed, would represent clear evidence of physics beyond the Standard Model, opening the door to an entirely new horizon,” says Alessandro Baldini, researcher at INFN Pisa, co-spokesperson of the international MEG II Collaboration.

The new analysis of MEG II data did not reveal any significant excess of events compared to the expected background. As a result, a new upper limit on the probability of this process has been established, which is currently the most stringent in the world. The new results, based on data collected in 2021 and 2022, are described in a paper published on arXiv [link] and submitted to the journal Physical Review Letters.

In the MEG II experiment, muons from the world’s most intense continuous muon beam are stopped on a thin target placed at the center of a superconducting magnet. The decay products are tracked by cutting-edge detectors: an ultra-light gas drift chamber and a series of scintillating plastic tiles reconstruct the positron’s trajectory and time of flight, while photons are detected using a 900-liter liquid xenon calorimeter.

The new MEG II result updates and improves the previous limit, which was obtained by combining data from the earlier MEG experiment with 2021 data from MEG II and presented in 2023 [link]. This improvement is due to the larger data sample collected in 2022, which is four times greater than that of 2021 alone, marking the first measurement based entirely on data from MEG II.

MEG II continued data taking in 2023 and 2024 and will proceed in the 2025–2026 period as well. The final MEG II dataset is expected to be about four times larger than the one currently presented. The goal is to improve the sensitivity to this decay by one order of magnitude compared to the predecessor experiment, MEG.

The MEG II collaboration includes over 70 physicists from research institutions in Italy, Japan, the United Kingdom, Russia, Switzerland, and the United States, including INFN. Italian researchers have played a leading role, guiding the construction and operation of the positron detectors.

 

 

 

 

 

 

Immagine: MEG II ©PSI MEG II ©PSI.

You might also be interested in

Research infrastructures shaping the future. A moment of the public event "Driving knowledge and innovation for tomorrow's communities" hosted by the Italy Pavilion at Expo2025 Osaka.

Major research infrastructures and Italy-Japan collaboration in fundamental physics at Expo2025 Osaka

Asimmetrie: The new issue is dedicated to the constants of physics

ALICE measures the conversion of lead into gold using Italian calorimeters

Laura Zani, INFN researcher at the Roma 3 Section and winner of the Young Experimental Physicist Prize 2025

Young Experimental Physicist Prize 2025 awarded to INFN researcher Laura Zani

PADME experiment_Frascati National Laboratories_INFN

New results from the Padme experiment in the search for the X17 particle

Hot aisle of the machine room at the INFN Turin computing center.

Computing Technologies for the Einstein Telescope: CTLAB4ET Laboratory inaugurated in Turin