Quadrupole collectivity in neutron-deficient Sn nuclei: 104Sn and the role of proton excitations

V. M. Bader,1,2 A. Gade,1,2 D. Weisshaar,1,2 B. A. Brown,1,2 T. Baugher,1,2 D. Bazin,1 J. S. Berryman,1 A. Ekström,1,3 M. Hjorth-Jensen,1,2,3 S. R. Stroberg,1,2 W. B. Walters,4 K. Wimmer,1,5 and R. Winkler1,* 1National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA 2Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA 3Department of Physics and Center of Mathematics for Applications, University of Oslo, N-0316 Oslo, Norway 4Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA 5Department of Physics, Central Michigan University, Mount Pleasant, Michigan 48859, USA (Received 1 July 2013; revised manuscript received 19 September 2013; published 4 November 2013)