The PIONEER experiment is a next-generation initiative aimed at measuring the branching ratio of charged pion decays to electrons vs. muons with unprecedented precision. This measurement holds significant potential for discovering new physics beyond the Standard Model (SM), particularly at high mass scales, and offers valuable insights into the universality of lepton interactions. Leveraging advanced instrumentation, refined from previous PEN and PiENu experiments, and a new high-intensity beam, PIONEER aims to improve upon previous precision by an order of magnitude, reaching the 10⁻⁴ level. Such precision would allow for a direct comparison with the SM prediction, which is similarly precise, where any deviation could unambiguously signal new physics. The experiment is further motivated by anomalies such as the muon g-2 discrepancy and hints of lepton flavor violation in the B-meson sector. Additionally, PIONEER will probe exotic rare decays involving sterile neutrinos and axions with unprecedented sensitivity.

Detector geometry simulations are well underway, and the experimental apparatus is being developed collaboratively by research teams from Canada, China, Germany, Japan, Mexico, Switzerland, and the USA. The detector will feature an 80 cm liquid Xenon sphere surrounding a beampipe and active target, promising to deliver cutting-edge data for both pion decays and rare exotic processes.