title: Nucleus ^{26}O: A Barely Unbound System beyond the Drip Line.
abstract: The unbound nucleus ^{26}O has been investigated using invariant-mass spectroscopy following one-proton removal reaction from a ^{27}F beam at 201  MeV/nucleon. The decay products, ^{24}O and two neutrons, were detected in coincidence using the newly commissioned SAMURAI spectrometer at the RIKEN Radioactive Isotope Beam Factory. The ^{26}O ground-state resonance was found to lie only 18±3(stat)±4(syst)  keV above threshold. In addition, a higher lying level, which is most likely the first 2^{+} state, was observed for the first time at 1.28_{-0.08}^{+0.11}  MeV above threshold. Comparison with theoretical predictions suggests that three-nucleon forces, pf-shell intruder configurations, and the continuum are key elements to understanding the structure of the most neutron-rich oxygen isotopes beyond the drip line.
authors.affiliation: Department of Physics, Tokyo Institute of Technology, 2-12-1 O-Okayama, Meguro, Tokyo 152-8551, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Kondo
authors.affiliation: Department of Physics, Tokyo Institute of Technology, 2-12-1 O-Okayama, Meguro, Tokyo 152-8551, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Nakamura
authors.affiliation: Department of Physics, Tokyo Institute of Technology, 2-12-1 O-Okayama, Meguro, Tokyo 152-8551, Japan.
authors.forename: R
authors.initials: R
authors.lastname: Tanaka
authors.affiliation: Department of Physics, Tokyo Institute of Technology, 2-12-1 O-Okayama, Meguro, Tokyo 152-8551, Japan.
authors.forename: R
authors.initials: R
authors.lastname: Minakata
authors.affiliation: Department of Physics, Tokyo Institute of Technology, 2-12-1 O-Okayama, Meguro, Tokyo 152-8551, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Ogoshi
authors.affiliation: LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, F-14050 Caen, France.
authors.forename: N A
authors.initials: NA
authors.lastname: Orr
authors.affiliation: LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, F-14050 Caen, France.
authors.forename: N L
authors.initials: NL
authors.lastname: Achouri
authors.affiliation: Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany.|ExtreMe Matter Institute EMMI and Research Division, GSI Helmholtzzentrum für Schwerionenforschung GmbH, D-64291 Darmstadt, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Aumann
authors.affiliation: RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Baba
authors.affiliation: LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, F-14050 Caen, France.
authors.forename: F
authors.initials: F
authors.lastname: Delaunay
authors.affiliation: RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
authors.forename: P
authors.initials: P
authors.lastname: Doornenbal
authors.affiliation: RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Fukuda
authors.affiliation: LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, F-14050 Caen, France.
authors.forename: J
authors.initials: J
authors.lastname: Gibelin
authors.affiliation: Department of Physics and Astronomy, Seoul National University, 599 Gwanak, Seoul 151-742, Republic of Korea.
authors.forename: J W
authors.initials: JW
authors.lastname: Hwang
authors.affiliation: RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Inabe
authors.affiliation: RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Isobe
authors.affiliation: RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
authors.forename: D
authors.initials: D
authors.lastname: Kameda
authors.affiliation: Department of Physics, Tokyo Institute of Technology, 2-12-1 O-Okayama, Meguro, Tokyo 152-8551, Japan.
authors.forename: D
authors.initials: D
authors.lastname: Kanno
authors.affiliation: Department of Physics and Astronomy, Seoul National University, 599 Gwanak, Seoul 151-742, Republic of Korea.
authors.forename: S
authors.initials: S
authors.lastname: Kim
authors.affiliation: Department of Physics, Tokyo Institute of Technology, 2-12-1 O-Okayama, Meguro, Tokyo 152-8551, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Kobayashi
authors.affiliation: Department of Physics, Tohoku University, Miyagi 980-8578, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Kobayashi
authors.affiliation: RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Kubo
authors.affiliation: LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, F-14050 Caen, France.
authors.forename: S
authors.initials: S
authors.lastname: Leblond
authors.affiliation: RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
authors.forename: J
authors.initials: J
authors.lastname: Lee
authors.affiliation: LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, F-14050 Caen, France.
authors.forename: F M
authors.initials: FM
authors.lastname: Marqués
authors.affiliation: RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Motobayashi
authors.affiliation: Departiment of Physics, Rikkyo University, Toshima, Tokyo 171-8501, Japan.
authors.forename: D
authors.initials: D
authors.lastname: Murai
authors.affiliation: Department of Physics, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Murakami
authors.affiliation: Department of Physics, Tohoku University, Miyagi 980-8578, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Muto
authors.affiliation: Department of Physics, Tokyo Institute of Technology, 2-12-1 O-Okayama, Meguro, Tokyo 152-8551, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Nakashima
authors.affiliation: Department of Physics, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Nakatsuka
authors.affiliation: Grand Accélérateur National d'Ions Lourds (GANIL), CEA/DRF-CNRS/IN2P3, Bvd Henri Becquerel, 14076 Caen, France.
authors.forename: A
authors.initials: A
authors.lastname: Navin
authors.affiliation: Department of Physics, Tokyo Institute of Technology, 2-12-1 O-Okayama, Meguro, Tokyo 152-8551, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Nishi
authors.affiliation: RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Otsu
authors.affiliation: RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Sato
authors.affiliation: Department of Physics and Astronomy, Seoul National University, 599 Gwanak, Seoul 151-742, Republic of Korea.
authors.forename: Y
authors.initials: Y
authors.lastname: Satou
authors.affiliation: RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Shimizu
authors.affiliation: RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Suzuki
authors.affiliation: Department of Physics, Tohoku University, Miyagi 980-8578, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Takahashi
authors.affiliation: RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Takeda
authors.affiliation: RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Takeuchi
authors.affiliation: Department of Physics, Tokyo Institute of Technology, 2-12-1 O-Okayama, Meguro, Tokyo 152-8551, Japan.|ExtreMe Matter Institute EMMI and Research Division, GSI Helmholtzzentrum für Schwerionenforschung GmbH, D-64291 Darmstadt, Germany.
authors.forename: Y
authors.initials: Y
authors.lastname: Togano
authors.affiliation: Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom.
authors.forename: A G
authors.initials: AG
authors.lastname: Tuff
authors.affiliation: Institut de Physique Nucléaire, Université Paris-Sud, IN2P3-CNRS, Université de Paris Sud, F-91406 Orsay, France.
authors.forename: M
authors.initials: M
authors.lastname: Vandebrouck
authors.affiliation: RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Yoneda