Pairing Forces Govern Population of Doubly Magic Ca 54 from Direct Reactions

• Published in: Physical review letters 2021-06, Vol.126 (25), Article 252501
• Main Authors: Browne, F., Chen, S., Doornenbal, P., Obertelli, A., Ogata, K., Utsuno, Y., Yoshida, K., Achouri, N. L., Baba, H., Calvet, D., Château, F., Chiga, N., Corsi, A., Cortés, M. L., Delbart, A., Gheller, J-M., Giganon, A., Gillibert, A., Hilaire, C., Isobe, T., Kobayashi, T., Kubota, Y., Lapoux, V., Liu, H. N., Motobayashi, T., Murray, I., Otsu, H., Panin, V., Paul, N., Rodriguez, W., Sakurai, H., Sasano, M., Steppenbeck, D., Stuhl, L., Sun, Y. L., Togano, Y., Uesaka, T., Wimmer, K., Yoneda, K., Aktas, O., Aumann, T., Boretzky, K., Caesar, C., Chung, L. X., Flavigny, F., Franchoo, S., Gasparic, I., Gerst, R.-B., Gibelin, J., Hahn, K. I., Holl, M., Kahlbow, J., Kim, D., Körper, D., Koiwai, T., Kondo, Y., Koseoglou, P., Lee, J., Lehr, C., Linh, B. D., Lokotko, T., MacCormick, M., Miki, K., Moschner, K., Nakamura, T., Park, S. Y., Rossi, D., Sahin, E., Schindler, F., Simon, H., Söderström, P-A., Sohler, D., Takeuchi, S., Törnqvist, H., Tscheuschner, J., Vaquero, V., Wagner, V., Wang, S., Werner, V., Xu, X., Yamada, H., Yan, D., Yang, Z., Yasuda, M., Zanetti, L.
• Format: Article
• Language: English
• ISSN: 0031-9007; 1079-7114; 1079-7114
• DOI: 10.1103/PhysRevLett.126.252501

Direct proton-knockout reactions of Sc-55 at similar to 220 MeV/nucleon were studied at the RIKEN Radioactive Isotope Beam Factory. Populated states of Ca-54 were investigated through -ray and invariant-mass spectroscopy. Level energies were calculated from the nuclear shell model employing a phenomenological intemucleon interaction. Theoretical cross sections to states were calculated from distorted-wave impulse approximation estimates multiplied by the shell model spectroscopic factors, which describe the wave function overlap of the Sc-55 ground state with states in Ca-54. Despite the calculations showing a significant amplitude of excited neutron configurations in the ground-state of Sc-55, valence proton removals populated predominantly the ground state of Ca-54. This counterintuitive result is attributed to pairing effects leading to a dominance of the ground-state spectroscopic factor. Owing to the ubiquity of the pairing interaction, this argument should be generally applicable to direct knockout reactions from odd-even to even-even nuclei.