Beyond the Neutron Drip-Line: The Unbound Oxygen Isotopes 25O and 26O

Caesar, C. and Simonis, J. and Adachi, T. and Aksyutina, Y. and Alcantara, J. and Altstadt, S. and Alvarez-Pol, H. and Ashwood, N. and Aumann, T. and Avdeichikov, V. and Barr, M. and Beceiro, S. and Bemmerer, D. and Benlliure, J. and Bertulani, C. A. and Boretzky, K. and Borge, M. J. G. and Burgunder, G. and Caamano, M. and Casarejos, E. and Catford, W. and Cederkaell, J. and Chakraborty, S. and Chartier, M. and Chulkov, L. and Cortina-Gil, D. and Pramanik, U. Datta and Fernandez, P. Diaz and Dillmann, I. and Elekes, Zoltán (2013) Beyond the Neutron Drip-Line: The Unbound Oxygen Isotopes 25O and 26O. PHYSICAL REVIEW C, 88 (3). ISSN 2469-9985

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Abstract

The very neutron-rich oxygen isotopes 25O and 26O are investigated experimentally and theoretically. The unbound states are populated in an experiment performed at the R3B-LAND setup at GSI via proton-knockout reactions from 26F and 27F at relativistic energies around 442 MeV/nucleon and 414 MeV/nucleon, respectively. From the kinematically complete measurement of the decay into 24O plus one or two neutrons, the 25O ground-state energy and width are determined, and upper limits for the 26O ground-state energy and lifetime are extracted. In addition, the results provide indications for an excited state in 26O at around 4 MeV. The experimental findings are compared to theoretical shell-model calculations based on chiral two and three-nucleon (3N) forces, including for the first time residual 3N forces, which are shown to be amplified as valence neutrons are added.

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