Direct Experimental Evidence for Strong Admixture of Different Parity States in Li-11

H. Simon,1 D. Aleksandrov,2 T. Aumann,3 L. Axelsson,4 T. Baumann,5 M. J. G. Borge,6 L. V. Chulkov,2 R. Collatz,5 J. Cub,1 W. Dostal,3 B. Eberlein,3 Th. W. Elze,7 H. Emling,5 H. Geissel,5 A. Grunschloss,7 M. Hellstrom,5 J. Holeczek,8 R. Holzmann,5 B. Jonson,4 J. V. Kratz,3 G. Kraus,5 R. Kulessa,9 Y. Leifels,5 A. Leistenschneider,7 T. Leth,10 I. Mukha,2,10 G. Munzenberg,5 F. Nickel,5 T. Nilsson,11 G. Nyman,4 B. Petersen,10 M. Pfutzner,5 A. Richter,1 K. Riisager,10 C. Scheidenberger,5 G. Schrieder,1 W. Schwab,5 M. H. Smedberg,4 J. Stroth,7 A. Surowiec,8 O. Tengblad,6 and M. V. Zhukov2,4 1Institut fur Kernphysik, Technische Universitat, D-64289 Darmstadt, Germany 2Kurchatov Institute, R-123182 Moscow, Russia 3Institut fur Kernchemie, Johannes Gutenberg-Universitat, D-55099 Mainz, Germany 4Fysiska Institutionen, Chalmers Tekniska Hogskola och Goteborgs Universitet, S-412 96 Goteborg, Sweden 5Gesellschaft fur Schwerionenforschung (GSI), D-64291 Darmstadt, Germany 6Institudo Estructura de la Materia, CSIC, E-28006 Madrid, Spain 7Institut fur Kernphysik, Johann-Wolfgang-Goethe-Universitat, D-60486 Frankfurt, Germany 8Institute of Physics, University of Silesia, PL-40-007 Katowice, Poland 9Instytut Fizyki, Uniwersytet Jagellonski, PL-30-059 Krakow, Poland 10Institut for Fysik og Astronomi, Aarhus Universitet, DK-8000 Aarhus C, Denmark 11EP Division, CERN, CH-1211, Geneve 23, Switzerland (Received 9 December 1998) Peripheral fragmentation of a 287 MeV nucleon beam of the halo nucleus 11Li incident on a carbon target has been studied in a fragment-neutron coincidence experiment. The momentum distribution of the 10Li fragments gives access to the momentum distribution of the removed neutron in 11Li. From the shape of the distribution, the 1s1 2 2 contribution to the mixture of 1s1 2 2 and 0p1 2 2 components in the ground-state wave function was determined to be 45 6 10 %. The angular correlation between the knocked out neutron and the one from the decay of 10Li shows a skew distribution signaling interference of these two different parity states.