Nature of seniority symmetry breaking in the semimagic nucleus Ru-94

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Sánchez Tembleque, Víctor
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Amer Physical Soc
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Direct lifetime measurements via gamma -gamma coincidences using a fast timing detector array consisting of LaBr3(Ce) scintillators has been applied to determine the lifetime of low-lying states in the semimagic (N = 50) nucleus Ru-94. The experiment was carried out as the first in a series of "FAIR-0" experiments with the DESPEC experimental setup at the Facility for Antiproton and Ion Research (FAIR). Excited states in Ru-94 were populated primarily via the beta-delayed proton emission of Pd-95 nuclei, produced in the projectile fragmentation of an 850 MeV/nucleon Xe-124 beam impinging on a 4 g/cm(2) Be-9 target. While the deduced E2 strength for the 2(+) -> 0(+) transition in the yrast cascade follows the expected behavior for conserved seniority symmetry, the intermediate 4(+) -> 2(+) transition exhibits a drastic enhancement of transition strength in comparison with pure-seniority model predictions as well as standard shell model predictions in the f pg proton hole space with respect to doubly magic Sn-100. The anomalous behavior is ascribed to a subtle interference between the wave function of the lowest seniority v = 2, I-pi = 4(+) state and that of a close-lying v = 4 state that exhibits partial dynamic symmetry. In addition, the observed strongly prohibitive 6(+) -> 4(+) transition can be attributed to the same mechanism but with a destructive interference. It is noted that such effects may provide stringent tests of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations.
Artículo firmado por 87 autores. The authors would like to thank the staff of the FRS and the GSI accelerator, for their excellent support. This work was supported by the Swedish Research Council under Grants No. 621-2014-5558 and No. 2019-04880. Support by the STFC under Grants No. ST/G000697/1, No. ST/P005314, and No. ST/P003982/1; by the UK Department for Business, Energy and Industrial Strategy via the National Measurement Office; by the BMBF under Grants No. 05P19RDFN1 and No. 05P21RDFN1; by the Helmholtz Research Academy Hesse for FAIR (HFHF); by the GSI F&E Grant No. KJOLIE1820; and by BMBF grant 05P19PKFNA are also acknowledged. P.H.R. and R.S. acknowledge support from the National Measurement System program unit of the UK's Department for BGS. G.H, M.S, and R.L. acknowledge IN2P3-GSI agreements, ADI-IDEX, and CSC-UPS grants. L.M.F. acknowledges the Spanish MICINN via Project No. RTI2018-098868-B-100. A.A. acknowledges partial support of the Ministerio de Ciencia e Innovación Grant No. PID2019-104714GB-C21.
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