Extended neutron orbital and the shell closure in Ca

Enciu, M.*; Liu, H. N.*; Obertelli, A.*; Doornenbal, P.*; Nowacki, F.*; Ogata, Kazuyuki*; Poves, A.*; Yoshida, Kazuki   ; Achouri, N. L.*; Baba, Hidetada*; Browne, F.*; Calvet, D.*; Chteau, F.*; Chen, S.*; 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.*; 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.*; Chung, L. X.*; Flavigny, F.*; Franchoo, S.*; Gasparic, I.*; Gerst, R.-B.*; Gibelin, J.*; Hahn, K. I.*; Kim, D.*; Kondo, Yosuke*; Koseoglou, P.*; Lee, J.*; Lehr, C.*; Li, P. J.*; Linh, B. D.*; Lokotko, T.*; MacCormick, M.*; Moschner, K.*; Nakamura, Takashi*; Park, S. Y.*; Rossi, D.*; Sahin, E.*; Sderstrm, P.-A.*; Sohler, D.*; Takeuchi, Satoshi*; Toernqvist, H.*; Vaquero, V.*; Wagner, V.*; Wang, S.*; Werner, V.*; Xu, X.*; Yamada, Hiroki*; Yan, D.*; Yang, Z.*; Yasuda, Masahiro*; Zanetti, L.*

The one-neutron knockout from Ca was performed at 230 MeV/nucleon combined with prompt spectroscopy. The momentum distributions corresponding to the removal of and neutrons were measured. The cross sections are consistent with a shell closure at the neutron number , found as strong as at and in Ca isotopes from the same observables. The analysis of the momentum distributions leads to a difference of the root-mean-square radii of the neutron and orbitals of 0.61(23) fm, in agreement with the modified-shell-model prediction of 0.7 fm suggesting that the large root-mean-square radius of the orbital in neutron-rich Ca isotopes is responsible for the unexpected linear increase of the charge radius with the neutron number.