A search is conducted for a new beyond-the-Standard-Model boson using events where a Higgs boson with mass 125 GeV decays to four leptons ($\ell =$ $e$ or $\mu$). This decay is presumed to occur via an intermediate state which contains one or two on-shell, promptly decaying bosons: $H\rightarrow ZX/XX \rightarrow 4\ell$, where $X$ is a new vector boson $Z_d$ or pseudoscalar $a$ with mass between 1 and 60 GeV... (read more)
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