Pairing Forces Govern Population of Doubly Magic $^{54}$Ca from Direct Reactions

F. Browne , S. Chen , P. Doornenbal , A. Obertelli (1) , K. Ogata , Y. Utsuno , K. Yoshida , N.L. Achouri (2) , H. Baba , D. Calvet (1) , F. Château (1) , N. Chiga , A. Corsi (1) , M.L. Cortés , A. Delbart (1) , J-M. Gheller (1) , A. Giganon (1) , A. Gillibert (1) , C. Hilaire (1) , T. Isobe , T. Kobayashi , Y. Kubota , V. Lapoux (1) , H.N. Liu (1) , T. Motobayashi , I. Murray (3) , H. Otsu , V. Panin , N. Paul (1) , W. Rodriguez , H. Sakurai , M. Sasano , D. Steppenbeck , L. Stuhl , Y.L. Sun (1) , Y. Togano , T. Uesaka , K. Wimmer , K. Yoneda , O. Aktas , T. Aumann , K. Boretzky , C. Caesar , L.X. Chung , F. Flavigny (3) , S. Franchoo (3) , I. Gasparic , R.-B. Gerst , J. Gibelin (2) , K.I. Hahn , M. Holl , J. Kahlbow , D. Kim , D. Körper , T. Koiwai , Y. Kondo , P. Koseoglou , J. Lee , C. Lehr , B.D. Linh , T. Lokotko , M. Maccormick (3) , K. Miki , K. Moschner , T. Nakamura , S.Y. Park , D. Rossi , E. Sahin , F. Schindler , H. Simon , P-A. Söderström , D. Sohler , S. Takeuchi , H. Törnqvist , J. Tscheuschner , V. Vaquero , V. Wagner , S. Wang , V. Werner , X. Xu , H. Yamada , D. Yan , Z. Yang , M. Yasuda , L. Zanetti

1 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers
2 LPCC - Laboratoire de physique corpusculaire de Caen
3 IPNO - Institut de Physique Nucléaire d'Orsay

Direct proton-knockout reactions of ${}^{55}\mathrm{Sc}$ at $\sim 220\mathrm{MeV}/\mathrm{nucleon}$ were studied at the RIKEN Radioactive Isotope Beam Factory. Populated states of ${}^{54}\mathrm{Ca}$ were investigated through $\gamma$-ray and invariant-mass spectroscopy. Level energies were calculated from the nuclear shell model employing a phenomenological internucleon 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 ${}^{55}\mathrm{Sc}$ ground state with states in ${}^{54}\mathrm{Ca}$. Despite the calculations showing a significant amplitude of excited neutron configurations in the ground-state of ${}^{55}\mathrm{Sc}$, valence proton removals populated predominantly the ground state of ${}^{54}\mathrm{Ca}$. 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.

Domains: Nuclear Theory [nucl-th]

F. Browne, S. Chen, P. Doornenbal, A. Obertelli, K. Ogata, et al.. Pairing Forces Govern Population of Doubly Magic $^{54}$Ca from Direct Reactions. Phys.Rev.Lett., 2021, 126 (25), pp.252501. ⟨10.1103/PhysRevLett.126.252501⟩. ⟨hal-03273401⟩