Observation of a narrow structure in 1 H( γ , K S 0 ) X via interference with φ -meson production

We report observation of a narrow peak structure at $\ensuremath{\sim}$1.54 GeV with a Gaussian width $\ensuremath{\sigma}=6$ MeV in the missing mass of ${K}_{S}$ in the reaction $\ensuremath{\gamma}+p\ensuremath{\rightarrow}p{K}_{S}{K}_{L}$. The observed structure may be due to the interference between a strange (or antistrange) baryon resonance in the $p{K}_{L}$ system and the $\ensuremath{\varphi}({K}_{S}{K}_{L})$ photoproduction leading to the same final state. The statistical significance of the observed excess of events estimated as the log-likelihood ratio of the resonant signal + background hypothesis and the $\ensuremath{\varphi}$-production-based background-only hypothesis corresponds to $5.3\ensuremath{\sigma}$.