Search for the Θ+ Pentaquark in the Reaction γd→pK−K+n

A search for the Θ+ in the reaction γd→pK−K+n was completed using the CLAS detector at Jefferson Lab. A study of the same reaction, published earlier, reported the observation of a narrow Θ+ resonance. The present experiment, with more than 30 times the integrated luminosity of our earlier measurement, does not show any evidence for a narrow pentaquark resonance. The angle-integrated upper limit on Θ+ production in the mass range of 1.52–1.56  GeV/c2 for the γd→pK−Θ+ reaction is 0.3 nb (95% C.L.). This upper limit depends on assumptions made for the mass and angular distribution of Θ+ production. Using Λ(1520) production as an empirical measure of rescattering in the deuteron, the cross section upper limit for the elementary γn→K−Θ+ reaction is estimated to be a factor of 10 higher, i.e., ~3  nb (95% C.L.).