Andre Frankenthal: Probing low-mass physics with high-energy accelerators

The energy of particle accelerators has been on constant rise for about a century, with the LHC reaching a remarkable 13.6 TeV center-of-mass energy in 2022. Such high energies allow physicists to search for increasingly heavier states produced in particle collisions. However, plenty of new physics scenarios involve much lighter unknown particles, which could nevertheless be experimentally accessible by the beam-intense accelerators of today. In this talk, I will describe how the innovative “data-scouting” technique of the CMS experiment at CERN can be used to probe very rare phenomena, including the first observation of the rare muon double Dalitz decay of the eta meson (a particle with a mass of only 548 MeV). I will also discuss how these rare meson decays can be used to search for signs of new physics, such as the dark photon. On another front, I will present the first physics results of the PADME Collaboration, an experiment designed to search directly for dark photons using a beam of high-energy positrons at Laboratori Nazionali di Frascati, in Italy. I will conclude by highlighting PADME’s current efforts to obtain independent confirmation or refutation of X17, a hypothetical new particle with a mass of only 16.7 MeV that could explain recent anomalies in nuclear spectroscopic measurements