Hosted by: Jan Bernauer

Abstract: Decays of the neutral and long-lived η and η′ mesons provide a unique, flavour-conserving laboratory to test low-energy Quantum Chromodynamics and search for new physics beyond the Standard Model. They have drawn world-wide attention in recent years and have inspired broad experimental programs in different high-intensity-frontier centers. New experimental data will offer critical inputs to precisely determine the light quark mass ratios, η-η′ mixing parameters, and hadronic contributions to the anomalous magnetic moment of the muon. At the same time, they will provide a sensitive probe to search for new physics. This includes searches for hidden photons, light Higgs scalars, and axion-like particles that are complementary to the world-wide efforts to detect new light particles below the GeV mass scale, as well as tests of discrete symmetry violation. In this talk, we will give an update on recent theoretical developments, discuss the experimental opportunities, and identify future prospects of the field.