Evidence for the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mo>Θ</mml:mo><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>in the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>γ</mml:mi><mml:mi>d</mml:mi><mml:mo>→</mml:mo><mml:msup><mml:mi>K</mml:mi><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:msup><mml:mi>K</mml:mi><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup><mml:mi mathvariant="italic">pn</mml:mi></mml:mrow></mml:math>reaction by detecting<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mi>K</mml:mi><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:msup><mml:mi>K</mml:mi><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>pairs

The $\ensuremath{\gamma}d\ensuremath{\rightarrow}{K}^{+}{K}^{\ensuremath{-}}\mathit{pn}$ reaction has been studied to search for the evidence of the ${\ensuremath{\Theta}}^{+}$ by detecting ${K}^{+}{K}^{\ensuremath{-}}$ pairs at forward angles. The Fermi-motion-corrected ${\mathit{nK}}^{+}$ invariant mass distribution shows a narrow peak at $1.524\ifmmode\pm\else\textpm\fi{}0.002+0.003$ GeV/${c}^{2}$. The statistical significance of the peak calculated from a shape analysis is 5.1 \ensuremath{\sigma}, and the differential cross section for the $\ensuremath{\gamma}n\ensuremath{\rightarrow}{K}^{\ensuremath{-}}{\ensuremath{\Theta}}^{+}$ reaction is estimated to be $12\ifmmode\pm\else\textpm\fi{}2$ nb/sr in the photon energy range from 2.0 to 2.4 GeV in the LEPS angular range by assuming the isotropic production of the ${\ensuremath{\Theta}}^{+}$ in the $\ensuremath{\gamma}n$ center-of-mass system. The obtained results support the existence of the ${\ensuremath{\Theta}}^{+}$.