Search for $\Theta^+(1540)$ pentaquark in high statistics measurement of   $\gamma p \to \bar K^0 K^+ n$ at CLAS
  The exclusive reaction $\gamma p \to \bar K^0 K^+ n$ was studied in the photon energy range between 1.6-3.8 GeV searching for evidence of the exotic baryon $\Theta^+(1540)\to nK^+$. The decay to $nK^+$ requires the assignment of strangeness $S=+1$ to any observed resonance. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility corresponding to an integrated luminosity of 70 $pb^{-1}$. No evidence for the $\Theta^+$ pentaquark was found. Upper limits were set on the production cross section as function of center-of-mass angle and $nK^+$ mass. The 95% CL upper limit on the total cross section for a narrow resonance at 1540 MeV was found to be 0.8 nb. 
M. Battaglieri, R. De Vita, V. Kubarovsky, L. Guo, G.S. Mutchler, P.   Stoler, D.P. Weygand and the CLAS Collaboration