Pairing forces govern population of doubly magic Ca from direct reactions

Browne, F.*; Chen, S.*; Doornenbal, P.*; Obertelli, A.*; Ogata, Kazuyuki*; Utsuno, Yutaka   ; Yoshida, Kazuki   ; Achouri, N. L.*; Baba, Hidetada*; Calvet, D.*; Chteau, F.*; Chiga, Nobuyuki*; Corsi, A.*; Corts, M. L.*; Delbart, A.*; Gheller, J.-M.*; Giganon, A.*; Gillibert, A.*; Hilaire, C.*; Isobe, Tadaaki*; Kobayashi, Toshio*; Kubota, Yuki*; Lapoux, V.*; Liu, H. N.*; Motobayashi, Toru*; Murray, I.*; Otsu, Hideaki*; Panin, V.*; Paul, N.*; Rodriguez, W.*; Sakurai, Hiroyoshi*; Sasano, Masaki*; Steppenbeck, D.*; Stuhl, L.*; Sun, Y. L.*; Togano, Yasuhiro*; Uesaka, Tomohiro*; Wimmer, K.*; Yoneda, Kenichiro*; 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.*; Krper, D.*; Koiwai, Takuma*; Kondo, Yosuke*; Koseoglou, P.*; Lee, J.*; Lehr, C.*; Linh, B. D.*; Lokotko, T.*; MacCormick, M.*; Miki, K.*; Moschner, K.*; Nakamura, Takashi*; Park, S. Y.*; Rossi, D.*; Sahin, E.*; Schindler, F.*; Simon, H.*; Sderstrm, P.-A.*; Sohler, D.*; Takeuchi, Satoshi*; Trnqvist, H.*; Tscheuschner, J.*; Vaquero, V.*; Wagner, V.*; Wang, S.*; Werner, V.*; Xu, X.*; Yamada, Hiroki*; Yan, D.*; Yang, Z.*; Yasuda, Masahiro*; Zanetti, L.*

Direct proton-knockout reactions of Sc were studied at the RIKEN Radioactive Isotope Beam Factory. Populated states of Ca were investigated through -ray and invariant-mass spectroscopy. Level energies were calculated from the nuclear shell model employing a phenomenological inter-nucleon interaction. Theoretical cross sections to states were calculated from distorted-wave impulse approximation estimates multiplied by the shell model spectroscopic factors. Despite the calculations showing a significant amplitude of excited neutron configurations in the ground-state of Sc, valence proton removals populated predominantly the ground-state of Ca. This counter-intuitive 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.