CERN's CMS Experiment Directly Observes Leptons Scattering from Protons After 50-Year Search

After more than five decades of research, the CMS experiment at CERN's Large Hadron Collider has directly observed evidence of protons emitting leptons (electrons, muons, and taus), a phenomenon predicted by the Standard Model. This observation, based on data collected between 2016 and 2026, provides the first strong evidence of muon-muon scattering and clarifies the lepton content of the proton, opening new avenues for physics beyond the Standard Model.