PIONEER 

Main Project: 

PIONEER, a rare pion decay experiment, will measure the branching ratio of pion’s rare decay channels with more precision to probe Beyond Standard Model (BSM) Physics. Presently the Standard Model (SM) prediction of the pion decaying to electron and muon is (1.2352±0.0002)*10^-4 and the best experimentally measured result is (1.2344 ± 0.0023(stat) ± 0.0019(syst)) × 10^−4. Even though the experimental result is in good agreement with SM prediction results from other experiments hint of Lepton Flavor Universality Violation (LFUV), which can explain the discrepancy seen in the measurement. PIONEER will attempt to improve the precision in experimental data and try to answer whether Lepton Flavor Universality is honored or not. The experiment will also try to precisely measure the branching ratio of the pion beta decay channel. The most precise measurement of this was done by PiBeta experiment at Paul Scherrer Institute (PSI), was not enough to solve the non-unitarity problem of CKM matrix. Improved precision of this measurement can solve this.

The experiment will be carried out at PSI in Switzerland at the pion beam line πE5. The pions will be stopped in a target, where the pions will decay. The target along with stopping the pions will locate the decay position and time, which makes it Active TARget or ATAR. The decay products will leave the ATAR and enter the Calorimeter, where the energy will be measured of the decay particles. The pacman shaped Calorimeter will cover most of the solid angle. The positrons directly coming from pion decay has a energy peak around 69 MeV, whereas the positrons coming from muon decay has maximum energy of 53 MeV. So, measuring the energy precisely is very important for the experiment, which has motivated the 20 radiation length LXe Calorimeter. The correlation between the ATAR hits and the Calorimeter will be established using the track reconstructed using the hits from the tracker.

To cover the same solid angle as the calorimeter, the experiment requires a tracker, which is a single volume hemi-spherical detector with very good spatial resolution. Micro-Resistive Well (μRWell) technology will be used for this. Two layers of μRWell detector with common cathode is being developed at Stony Brook University. Both simulation and hardware R&D on μRWell technology as well as designing and building of the detector is going on.

PIONEER