R. Sekiya, K. Itahashi, Y. K. Tanaka, S. Hirenzaki, N. Ikeno, V. Metag, M. Nanova, J. Yamagata-Sekihara, V. Drozd, H. Ekawa, H. Geissel, E. Haettner, A. Kasagi, E. Liu, M. Nakagawa, S. Purushothaman, C. Rappold, T. R. Saito, H. Alibrahim Alfaki, F. Amjad, M. Armstrong, K.-H. Behr, J. Benlliure, Z. Brencic, T. Dickel, S. Dubey, S. Escrig, M. Feijoo-Fontán, H. Fujioka, Y. Gao, F. Goldenbaum, A. Graña González, M. N. Harakeh, Y. He, H. Heggen, C. Hornung, N. Hubbard, M. Iwasaki, N. Kalantar-Nayestanaki, M. Kavatsyuk, E. Kazantseva, A. Khreptak, B. Kindler, H. Kollmus, D. Kostyleva, S. Kraft-Bermuth, N. Kurz, B. Lommel, S. Minami, D. J. Morrissey, P. Moskal, I. Mukha, C. Nociforo, H. J. Ong, S. Pietri, E. Rocco, J. L. Rodríguez-Sánchez, P. Roy, R. Ruber, S. Schadmand, C. Scheidenberger, P. Schwarz, V. Serdyuk, M. Skurzok, B. Streicher, K. Suzuki, B. Szczepanczyk, X. Tang, N. Tortorelli, M. Vencelj, T. Weber, H. Weick, M. Will, K. Wimmer, A. Yamamoto, A. Yanai, J. Zhao
The missing mass of the ^{12}C(p,d) reaction has been measured near the η^{'}-meson emission threshold in coincidence with a high-momentum proton to selectively collect η^{'}-^{11}C mesic nucleus formation events at GSI, Germany. A 2.5 GeV proton excites a carbon nucleus in order to form an η^{'}-mesic nucleus emitting a deuteron forward with an energy of ∼1.5 GeV. The deuteron is momentum analyzed by the fragment separator used as a high-resolution spectrometer to deduce the excitation energy of the residual system. The large-acceptance detector WASA surrounding the target identifies high-momentum protons emitted in the decay of the η^{'}-mesic nucleus. The measured semiexclusive spectrum exhibits structures below the threshold though the statistical significance is limited. The spectrum is fitted by theoretically calculated spectra varying optical-potential parameters of the η^{'}-nucleus interaction. The analysis results indicate possible formation of η^{'}-mesic nuclei for the real potential depth of ∼-61 MeV with a local statistical significance of 3.5σ and, taking into account the look-elsewhere effect, a global significance of 2.1σ.