Beyond the neutron drip line: The unbound oxygen isotopes O-25 and O-26

Beyond the neutron drip line: The unbound oxygen isotopes O-25 and O-26

Caesar, C.; Simonis, J.; Adachi, T.; Aksyutina, Y.; Alcantara, J.; Altstadt, S.; Alvarez-Pol, H.; Ashwood, N.; Aumann, T.; Avdeichikov, V.; Barr, M.; Beceiro, S.; Bemmerer, D.; Benlliure, J.; Bertulani, C.; Boretzky, K.; Borge, M.; Burgunder, G.; Caamano, M.; Casarejos, E.; Catford, W.; Cederkall, J.; Chakraborty, S.; Chartier, M.; Chulkov, L.; Cortina-Gil, D.; Pramanik, U.; Fernandez, P.; Dillmann, I.; Elekes, Z.; Enders, J.; Ershova, O.; Estrade, A.; Farinon, F.; Fraile, L.; Freer, M.; Freudenberger, M.; Fynbo, H.; Galaviz, D.; Geissel, H.; Gernhauser, R.; Golubev, P.; Diaz, D.; Hagdahl, J.; Heftrich, T.; Heil, M.; Heine, M.; Heinz, A.; Henriques, A.; Holl, M.; Holt, J.; Ickert, G.; Ignatov, A.; Jakobsson, B.; Johansson, H.; Jonson, B.; Kalantar-Nayestanaki, N.; Kanungo, R.; Kelic-Heil, A.; Knobel, R.; Kroll, T.; Krucken, R.; Kurcewicz, J.; Labiche, M.; Langer, C.; Le Bleis, T.; Lemmon, R.; Lepyoshkina, O.; Lindberg, S.; Machado, J.; Marganiec, J.; Maroussov, V.; Menendez, J.; Mostazo, M.; Movsesyan, A.; Najafi, A.; Nilsson, T.; Nociforo, C.; Panin, V.; Perea, A.; Pietri, S.; Plag, R.; Prochazka, A.; Rahaman, A.; Rastrepina, G.; Reifarth, R.; Ribeiro, G.; Ricciardi, M.; Rigollet, C.; Riisager, K.; Roder, M.; Rossi, D.; Del Rio, J.; Savran, D.; Scheit, H.; Schwenk, A.; Simon, H.; Sorlin, O.; Stoica, V.; Streicher, B.; Taylor, J.; Tengblad, O.; Terashima, S.; Thies, R.; Togano, Y.; Uberseder, E.; van de Walle, J.; Velho, P.; Volkov, V.; Wagner, A.; Wamers, F.; Weick, H.; Weigand, M.; Wheldon, C.; Wilson, G.; Wimmer, C.; Winfield, J.; Woods, P.; Yakorev, D.; Zhukov, M.; Zilges, A.; Zoric, M.; Zuber, K.

The very neutron-rich oxygen isotopes O-25 and O-26 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 F-26 and F-27 at relativistic energies around 442 and 414 MeV/nucleon, respectively. From the kinematically complete measurement of the decay into O-24 plus one or two neutrons, the O-25 ground-state energy and width are determined, and upper limits for the O-26 ground-state energy and lifetime are extracted. In addition, the results provide indications for an excited state in O-26 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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