Nature of seniority symmetry breaking in the semimagic nucleus <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Ru</mml:mi><mml:mprescripts/><mml:none/><mml:mn>94</mml:mn></mml:mmultiscripts></mml:math>

Direct lifetime measurements via $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidences using a fast timing detector array consisting of ${\mathrm{LaBr}}_{3}(\mathrm{Ce})$ scintillators has been applied to determine the lifetime of low-lying states in the semimagic $(N=50)$ nucleus $^{94}\mathrm{Ru}$. 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 $^{94}\mathrm{Ru}$ were populated primarily via the $\ensuremath{\beta}$-delayed proton emission of $^{95}\mathrm{Pd}$ nuclei, produced in the projectile fragmentation of an 850 MeV/nucleon $^{124}\mathrm{Xe}$ beam impinging on a 4 g/${\mathrm{cm}}^{2}\phantom{\rule{4pt}{0ex}}^{9}\mathrm{Be}$ target. While the deduced $E2$ strength for the ${2}^{+}\ensuremath{\rightarrow}{0}^{+}$ transition in the yrast cascade follows the expected behavior for conserved seniority symmetry, the intermediate ${4}^{+}\ensuremath{\rightarrow}{2}^{+}$ transition exhibits a drastic enhancement of transition strength in comparison with pure-seniority model predictions as well as standard shell model predictions in the $fpg$ proton hole space with respect to doubly magic $^{100}\mathrm{Sn}$. The anomalous behavior is ascribed to a subtle interference between the wave function of the lowest seniority $\ensuremath{\nu}=2$, ${I}^{\ensuremath{\pi}}={4}^{+}$ state and that of a close-lying $\ensuremath{\nu}=4$ state that exhibits partial dynamic symmetry. In addition, the observed strongly prohibitive ${6}^{+}\ensuremath{\rightarrow}{4}^{+}$ 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.