Evidence of the \Theta^+ in the \gamma d \to K^+K^-pn reaction

The gamma d -> K(+)K(-)pn reaction has been studied to search for the evidence of the Theta(+) by detecting K+K- pairs at forward angles. The Fermi-motion-corrected nK(+) invariant mass distribution shows a narrow peak at 1.524 +/- 0.002+0.003 GeV/c(2). The statistical significance of the peak calculated from a shape analysis is 5.1 sigma, and the differential cross section for the gamma n -> K-Theta(+) reaction is estimated to be 12 +/- 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 Theta(+) in the gamma n center-of-mass system. The obtained results support the existence of the Theta(+).