Quadrupole collectivity in Ca 42 from low-energy Coulomb excitation with AGATA

20 pags., 12 figs., 14 tabs.
A Coulomb-excitation experiment to study electromagnetic properties of Ca42 was performed using a 170-MeV calcium beam from the TANDEM XPU facility at INFN Laboratori Nazionali di Legnaro. γ rays from excited states in Ca42 were measured with the AGATA spectrometer. The magnitudes and relative signs of ten E2 matrix elements coupling six low-lying states in Ca42, including the diagonal E2 matrix elements of 21+ and 22+ states, were determined using the least-squares code gosia. The obtained set of reduced E2 matrix elements was analyzed using the quadrupole sum rule method and yielded overall quadrupole deformation for 01,2+ and 21,2+ states, as well as triaxiality for 01,2+ states, establishing the coexistence of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in Ca42. The experimental results were compared with the state-of-the-art large-scale shell-model and beyond-mean-field calculations, which reproduce well the general picture of shape coexistence in Ca42.
K.H.-K. acknowledges support from the Research Council of Norway under Grant No. 213442. T.R.R. acknowledges computing time at GSI-Darmstadt and support from Spanish MINECO under Programa Ramon y Cajal 11420 and FIS-2014-53434-P (T.R.R.). We also acknowledge the support by Generalitat Valenciana, Spain, under Grant No. PROMETEOII/2014/019 and by the FEDER funds of the European Commission (A. Gadea), Spanish Ministerio de Economía y Competitividad under contract FPA2014-57196-C5 (A. Jungclaus, A Gadea), German Bundesministerium für Bildung und Forschung (BMBF) under Contract No. 05P12PKFNE TP4 (B. Birkenbach), the Polish National Science Centre under Projects No. 2011/03/B/ST2/01894, No. DEC-2013/10/M/ST2/00427, No. 2013/08/M/ST2/00591, No. UMO-2014/14/M/ST2/00738 (COPIN-INFN Collaboration), No. 2015/17/B/ST2/01534, No. 2016/22/M/ST200269, the UK STFC under Grants No. ST/J000124/1 and No. ST/L005735/1. The EAGLE Collaboration thanks the European Gamma-Ray Spectroscopy Pool (GAMMAPOOL) for the loan of Ge detectors.