The study of high-efficiency pion production

Weichao Yao1,a , Masaharu Aoki1, Chen Wu2,3, Kou Oishi4,5, Yoshinori Fukao4

1 Department of Physics, Graduate School of Science, Osaka University, Osaka 560043, Japan
2 Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
3 Spallation Neutron Source Science Center, Dongguan 523808, China
4 High Energy Accelerator Research Organization (KEK), Tsukuba, Japan
5 Imperial College London, London, UK

Eur. Phys. J. Plus (2025) 140:267
4/2/25
https://doi.org/10.1140/epjp/s13360-025-06164-9

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.

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