Search for the θ+ pentaquark via the π-p→K-X reaction at 1.92GeV/c

The Theta^{+} pentaquark baryon was searched for via the pi^{-}pK^{-}X reaction with a missing mass resolution of 1.4MeV/c^{2} (FWHM) at the Japan Proton Accelerator Research Complex (J-PARC). pi^{-} meson beams were incident on the liquid hydrogen target with a beam momentum of 1.92GeV/c. No peak structure corresponding to the Theta^{+} mass was observed. The upper limit of the production cross section averaged over the scattering angle of 2° to 15° in the laboratory frame is obtained to be 0.26mub/sr in the mass region of 1.51-1.55GeV/c^{2}. The upper limit of the Theta^{+} decay width is obtained to be 0.72 and 3.1MeV for J_{Theta}^{P}=1/2^{+} and J_{Theta}^{P}=1/2^{-}, respectively, using the effective Lagrangian approach.