The Pentaquark $\Theta^+$ in $nK^+$ and $pK^0_S$, and its $\Sigma^+_5$   partner
  A systematic lowering in mass of strangeness ambiguous $pK^0_S$ peaks relative to the $nK^+$ is noted. We discuss how measurement of $\gamma p\to \Theta^+ K^0_S\to p K^0_S K^0_S \to p\pi^+\pi^-\pi^+\pi^-$ in association with $\gamma p\to \Theta^+ K^0_S\to n K^+ K^0_S$ can help to clarify the nature of the narrow baryon state claimed in $p K^0_S$ invariant mass distributions. This can both establish the $\Theta^+$ in a single experiment and also reveal, or place severe limits on, the existence of an associated $\Sigma_5$ pentaquark. 
Qiang Zhao and Frank E. Close