A double-$Lambda$ hypernucleus, ${}_{LambdaLambda}mathrm{Be}$, was observed by the J-PARC E07 collaboration in nuclear emulsions tagged by the $(K^{-},K^{+})$ reaction. This event was interpreted as a production and decay of $ {}_{LambdaLambda}^{;10}mathrm{Be}$, ${}_{LambdaLambda}^{;11}mathrm{Be}$, or ${}_{LambdaLambda}^{;12}mathrm{Be}^{*}$ via $Xi^{-}$ capture in ${}^{16}mathrm{O}$. By assuming the capture in the atomic 3D state, the binding energy of two $Lambda$ hyperons$,$($B_{LambdaLambda}$) of these double-$Lambda$ hypernuclei are obtained to be $15.05 pm 0.11,mathrm{MeV}$, $19.07 pm 0.11,mathrm{MeV}$, and $13.68 pm 0.11,mathrm{MeV}$, respectively. Based on the kinematic fitting, ${}_{LambdaLambda}^{;11}mathrm{Be}$ is the most likely explanation for the observed event.
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