Search for the $Θ^+$ pentaquark in the reaction $γd \to p K^- K^+ n$

Abstract

A search for the \thp in the reaction $γd \to pK^-K^+n$ was completed using the CLAS detector at Jefferson Lab. A study of the same reaction, published earlier, reported the observation of a narrow \thp 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 \thp production in the mass range of 1.52 to 1.56 GeV/c$^2$ for the $γd \to pK^-Θ^+$ reaction is 0.3 nb (95% CL). This upper limit depends on assumptions made for the mass and angular distribution of \thp production. Using \lamstar production as an empirical measure of rescattering in the deuteron, the cross section upper limit for the elementary $γn \to K^-Θ^+$ reaction is estimated to be a factor of 10 higher, {\it i.e.}, $\sim 3$ nb (95% CL).