Measurement of the charged-pion branching ratio to electrons vs. muons Re/μ is extremely sensitive to a wide variety of new physics effects. The precision of the SM prediction for Re/μ is ~1 part in 10^4, 15 times more precise than the current experimental result. A next-generation experiment, PIONEER, is aiming at reducing the precision gap between theory and experiment, testing lepton flavor universality at an unprecedented level, and probing new physics mass scales up to the PeV range. Additionally PIONEER is aiming at a 3 to 10-fold improvement in the pion beta decay, π+ → π0e+ν(γ) measurement which determines |V_ud| in a theoretically pristine manner. This measurement would shed new lights on recently emerged tensions in CKM unitarity. PIONEER will use a combination of new detector technologies based an LGAD silicon tracking target, a deep calorimeter (the leading contender being a large LXe quasi-sphere) with high solid angle coverage and high-speed electronics to optimize its energy and time resolution with respect to previous experiments. I’ll discuss existing results and present PIONEER’s detector concept and experimental goals.
