Nuclear structures near and beyond the neutron drip line studied by breakup reactions at SAMURAI at RIBF

Some of the first results from kinematically complete measurements of breakup reactions on neutron-rich boron to oxygen isotopes, along and beyond the neutron drip line, are presented and discussed. These experiments were performed at the recently-commissioned large-acceptance multi-purpose spectrometer SAMURAI ({\bf S}uperconducting {\bf A}nalyser for {\bf MU}lti-particles from {\bf Ra}dio-{\bf I}sotope Beam) at the new-generation RI beam facility, RIBF, at RIKEN. The experiments aimed at probing the two-neutron Borromean halo nuclei, $^{19}$B and $^{22}$C, and at exploring the heavy oxygen isotopes, $^{25,26}$O, which are beyond the neutron drip line. The study of $^{19}$B and $^{22}$C has been made primarily by the Coulomb breakup, which is sensitive to the halo states and associated two-neutron correlations~[1,2]. $^{22}$C has drawn much attention due to the possibility that it has the largest halo known~[3]. In addition, $^{22}$C may also exhibit features consistent with the new magic number $N$=16, as was recently suggested by our inclusive measurement of the momentum distribution of $^{20}$C following breakup on a C target~[4]. $^{25}$O and $^{26}$O have drawn much attention since these unbound nuclei may have keys to understand why the neutron drip line ends anomalously closer to the stability for oxygen isotopes. $^{25}$O and $^{26}$O have been produced by the proton removal reactions on $^{26}$F,$^{27}$Ne, and $^{27}$F,$^{28}$Ne, respectively, at 220-250 MeV/nucleon. Preliminary data are shown and discussed. Finally, some perspectives on future projects using the SAMURAI facility are presented. \bigskip \\ \noindent [1] T.~Nakamura, Y.~Kondo, Clusters in Nuclei Vol. 2, Lecture Notes in Physics Vol.848, Springer, ed. C.Beck (2012).\\ \noindent [2] T.~Aumann, T.~Nakamura, Phys.Scr. {\bf T152}, 014012 (2013).\\ \noindent [3] K.~Tanaka {\it et al.}, Phys. Rev. Lett. {\bf 104}, 062701 (2010).\\ \noindent [4] N.~Kobayashi, T.~Nakamura {\it et al.}, Phys. Rev. C {\bf 86}, 054604 (2012).