PIONEER, a rare pion decay experiment

Several inconsistencies between Standard Model (SM) predictions and experimental data, motivate PIONEER, the next-generation rare pion decay experiment. By probing the difference between decay of pion into electron and muon with a precision of 1 part in 10⁴ and the rare process of pion beta decay, with 3 to 10-fold improvement in sensitivity, the experiment aims to test the lepton flavor universality and CKM unitarity respectively, which is very important in light of the recently emerged tensions. The aimed precision requires excellent reconstruction of decay particles which the collaboration aims to achieve with a detector consisting of a segmented Low Gain Avalanche Detector (LGAD) based Active Target (ATAR), a Liquid Xenon Calorimeter of 25 radiation lengths and a gaseous detector based tracker. A GEANT based optimization study of a μ-RWell tracker surrounding the ATAR to achieve the required precision has been highlighted here.