[PRad] New X17 result from MEG-II

[Tyler Hague]

Hello everyone,

A colleague pointed me to a new X17 search result from the MEG-II collaboration after seeing a presentation on the topic this morning (presentation here<https://indico.psi.ch/event/16492/contributions/58338/attachments/31472/62746/MEGII_X17_PSI2025_AP.pdf>). Looking through our previous emails, I’m don’t think this was sent around before. I recall seeing a presentation on this at CIPANP this past June (here<https://agenda.hep.wisc.edu/event/2257/contributions/34090/attachments/10477/13485/iwamoto_cipanp_2025.pdf>). In the publication from July (here<https://link.springer.com/article/10.1140/epjc/s10052-025-14345-0>), MEG-II reports that they partially exclude the X17 hypothesis. See the paper for more details, their sensitivity varies throughout the mass window. They do not fully rule out the hypothesis and still leave plenty of room for us to improve upon the reach.

This is particularly interesting given that it seemingly is a different message from the preliminary PADME results that we’ve discussed.

Best,
Tyler
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