Neutron skin and signature of the = 14 Shell gap Found From Measured Proton Radii of N
S. Bagchi (GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany, Astronomy and Physics Department, Saint Mary's University, Halifax, Canada, Justus-Liebig University, Giessen, Germany); R. Kanungo (TRIUMF, Vancouver, Canada, Astronomy and Physics Department, Saint Mary's University, Halifax, Canada); W. Horiuchi (Department of Physics, Hokkaido University, Sapporo, Japan); G. Hagen (Department of Physics and Astronomy, University of Tennessee, Knoxville, USA, Physics Division, Oak Ridge National Laboratory, Oak Ridge, USA); T.D. Morris (Department of Physics and Astronomy, University of Tennessee, Knoxville, USA, Physics Division, Oak Ridge National Laboratory, Oak Ridge, USA); et al - Show all 40 authors
A thick neutron skin emerges from the first determination of root mean square radii of the proton distributions for $^{17−22}$N from charge changing cross section measurements around 900A MeV at GSI. Neutron halo effects are signalled for $^{22}$N from an increase in the proton and matter radii. The radii suggest an unconventional shell gap at N = 14 arising from the attractive proton–neutron tensor interaction, in good agreement with shell model calculations. Ab initio, in-medium similarity re-normalization group, calculations with a state-of-the-art chiral nucleon–nucleon and three-nucleon interaction reproduce well the data approaching the neutron drip-line isotopes but are challenged in explaining the complete isotopic trend of the radii.