Pairing Forces Govern Population of Doubly Magic ^{54}Ca from Direct Reactions
7 pags., 3 figs. ; Direct proton-knockout reactions of ^{55}Sc at ∼220 MeV/nucleon were studied at the RIKEN Radioactive Isotope Beam Factory. Populated states of ^{54}Ca were investigated through γ-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}Sc ground state with states in ^{54}Ca. Despite the calculations showing a significant amplitude of excited neutron configurations in the ground-state of ^{55}Sc, valence proton removals populated predominantly the ground state of ^{54}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. ; Our gratitude is extended to the RIKEN Nishina Center accelerator staff for the stable and high-intensity transport of the Zn primary beam, and the BigRIPS team for their preparation of the magnetic settings of the secondary beam. F. B. is supported by the RIKEN Special Postdoctoral Researcher Program. S. C. acknowledges support from the IPA program at the RIKEN Nishina Center. K. O. and K. Y. acknowledge the support from Grants-in-Aid of the Japan Society for the Promotion of Science under Grants No. JP16K05352. This work was supported by JSPS KAKENHI Grants No. JP16H02179 and No. JP18H05404, the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Grant No. BL 1513/1-1 HGS-HIRe and Project-ID 279384907-SFB 1245 and the GSI-TU Darmstadt cooperation agreement, the BMBF (Grant No. 05P19RDFN1), Swedish Research Council under Grants No. 621-2014-5558 and No. 2019-04880. L. X. C. and B. D. L. are supported by the Vietnam MOST via the Physics Development Program Grant No. TĐLCN.25/18. D. So. was supported by the European Regional Development Fund Contract No. GINOP-2.3.3-15-2016-00034 and the National Research, Development and Innovation Fund of Hungary via Project No. K128947. L. S, K. I. H., D. K., and S. Y. P. acknowledge the support from the IBS grant funded by the Korea government (No. IBS-R031-D1). ; Peer reviewed