Hori, M., Soter, A., Aghai-Khozani, H., Barna, D., Dax, A., Hayano, R. S., et al. (2015). Method for laser spectroscopy of metastable pionic helium atoms. Hyperfine Interactions, 233(1-3), 83-87. doi:10.1007/s10751-015-1163-7.