DREB2014 - Direct Reactions with Exotic Beams

The recent improvements in the experimental sensitivity have opened new avenues to study very neutron-rich isotopes of Carbon and Oxygen, allowing for an improved understanding of the structure of them. The present work aims at exploration of neutron- unbound states of 19C via a one neutron knockout reaction. A study of 19C utilizing in-beam γ-ray spectroscopy measurement reported that the 3/2+1 and 5/2+1 states are bound. On the other hand, in a study of inclusive one-neutron knockout cross section, argued that the experimental inclusive knockout cross section from 20C to 19C did not support the existence of the 5/2+1 state below the threshold. In this work, the invariant mass measurement in inverse kinematics was carried out in order to clarify the issue of bound/unbound nature of the 5/2+1 state. The experi- ment was performed at the RIBF facility in RIKEN. A 20C secondary beam produced by BigRIPS with an energy of 280 MeV/nucleon impinged on a carbon target placed before the SAMURAI spectrometer. By taking full advantage of the analyzer system comprised of a large-acceptance super-conducting dipole magnet, associated tracking de- tectors, and a large volume neutron detector system, an invariant mass spectrum for the system of 18C+n was reconstructed. Details of the measurement and analysis along with new results on the low-lying states of 19C will be presented.