Search for Pentaquarks at CLAS in Photoproduction from Protons

The CLAS Collaboration at Jefferson Lab has a comprehensive program to search for evidence of a pentaquark in photoproduction from protons and deuterons. Preliminary results from the first of this new round of experiments from a proton target are presented here. The experiment was run in May-July 2004, with a photon energy range from 1.5 to 3.8 GeV. It collected an integrated luminosity of about 70 pb$^{-1}$, which yielded more than an order of magnitude greater statistical precision than previously obtained. We report on the search for the possible reaction $\gamma p \rightarrow \bar{K}^{0} \Theta^{+}$, with $\Theta^{+} \rightarrow K^{+}n$. The $\bar{K}^{0}$ was reconstructed from the invariant mass of its detected $\pi^{+}$ and $\pi^{-}$ decay products, the $K^{+}$ was detected directly, and the undetected neutron $(n)$ was reconstructed from the missing 4-momenta of the detected particles. Preliminary results will be presented and compared with previously published data [1] in the same kinematic region. A second experiment on the proton focusing on higher energies (up to 6 GeV) is scheduled for next year. With ten times more statistics it will test our previously published [2] data on the proton for the possible existence of a pentaquark state in the reaction $\gamma p \rightarrow \pi^{+}K^{-}\Theta^{+}$. \newline \newline References \newline [1] J. Barth \textit{et al.}, Phys. Lett. B \textbf{572}, 127 (2003)\newline [2] V. Kubarovsky \textit{et al.}, Phys. Rev. Lett, \textbf{92}, 032001 (2004)