The study of high-efficiency pion production

An optimization study was conducted on low-energy pion production using a cylindrical tungsten target for the COMET Phase-II experiment, taking into account recent measurements of proton-beam emittance. The study suggests factor 1.6 of improvement in pion production efficiency by reducing the target radius down to 4 mm. This enhancement is attributed to the reduction in the emittance of the proton beam. Further increases in target radius simply reduce the yield of low-energy pions and, consequently, the stopping rate of low-energy muons in the muon stopping target. The analysis reveals that the pion production spectrum at higher momentum cannot compensate for the limitations imposed by the range-momentum curve of pions. There is a potential further improvement in low-energy pion production with an ideally narrow proton beam.