Synthesis of superheavy nuclei in the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow/><mml:mrow><mml:mn>48</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi mathvariant="normal">Ca</mml:mi><mml:mrow><mml:msup><mml:mrow><mml:mo>+</mml:mo></mml:mrow><mml:mrow><mml:mn>244</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi mathvariant="normal">Pu</mml:mi></mml:math>reaction:<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow/><mml:mrow><mml:mn>288</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mn>114</mml:mn></mml:math>

In the bombardment of a ${}^{244}\mathrm{Pu}$ target with ${}^{48}\mathrm{Ca}$ ions, we observed two identical decay sequences of genetically linked events, each consisting of an implanted heavy atom, two subsequent \ensuremath{\alpha} decays, and terminated by a spontaneous fission. The measured \ensuremath{\alpha} energies and corresponding half-lives of the sequential chain members were ${E}_{\ensuremath{\alpha}}=9.84\ifmmode\pm\else\textpm\fi{}0.05 \mathrm{MeV}$ ${(T}_{1/2}{=1.9}_{\ensuremath{-}0.8}^{+3.3} \mathrm{s})$ and $9.17\ifmmode\pm\else\textpm\fi{}0.05 \mathrm{MeV}$ ${(T}_{1/2}{=9.8}_{\ensuremath{-}3.8}^{+18} \mathrm{s});$ for the spontaneous fission ${(T}_{1/2}{=7.5}_{\ensuremath{-}2.9}^{+14} \mathrm{s}),$ the total energies deposited in the detector array were $213\ifmmode\pm\else\textpm\fi{}2$ and $221\ifmmode\pm\else\textpm\fi{}2 \mathrm{MeV}.$ The decay properties of the synthesized nuclei are consistent with the consecutive \ensuremath{\alpha} decays originating from the parent even-even nucleus ${}^{288}114,$ produced in the $4n$-evaporation channel with a cross section of about 1 pb. ${}^{288}114$ and ${}^{284}112$ are the heaviest known \ensuremath{\alpha}-decaying even-even nuclides, following the production of ${}^{260}\mathrm{Sg}$ and ${}^{266}\mathrm{Sg}$ $(Z=106)$ and the observation of \ensuremath{\alpha} decay of ${}^{264}\mathrm{Hs}$ $(Z=108).$ The observed radioactive properties of ${}^{288}114$ and the daughter nuclides match the decay scenario predicted by the macroscopic-microscopic theory.

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