Colliding light, tau g–2, and broadband axion detection

The muon anomalous magnetic moment (g–2) exhibits tantalising tensions with the Standard Model. But what about tau g–2? Remarkably, tau g–2 remains poorly constrained but can be 280 times more sensitive to new physics than the muon. Recently, ATLAS and CMS announced groundbreaking measurements of tau g–2 competitive with LEP. These exploit the landmark observation of tau pairs created via photon collisions in LHC heavy-ion data. Beyond colliders, limitations with existing axion searches motivate the Broadband Reflector Experiment for Axion Detection (BREAD) proposal at Fermilab. Quantum sensing progress enables BREAD to open multi-decade discovery sensitivity to axion dark matter above microwave frequencies that has long eluded conventional haloscopes. BREAD uses interdisciplinary innovations across astronomy, particle physics, and quantum technology.