A high-resolution (σinstr.=1.5 MeV) search for narrow states (ΓMeV) with masses of Mx≈1500–1850 MeV in ep→e′K+X,e′K-X, and e′π+X electroproduction at small angles and low Q2 was performed. These states would be candidate partner states of the reported Θ+(1540) pentaquark. No statistically significant signal was observed in any of the channels at 90% C.L. Upper limits on forward production were determined to be between 0.8% and 4.9% of the Λ(1520) production cross section, depending on the channel and the assumed mass and width of the state.
Qiang, Y.; Holmstrom, Timothy; and Jefferson Lab Hall Collaboration, "Search for Σ(5)(0), N(5)(0), and Θ++ Pentaquark States" (2007). Chemistry and Physics Faculty Publications. 8.
Phys. Rev. C 75, 055208 (2007)