Search for the Θ+ Pentaquark via the π- p → K- X Reaction at 1.92 GeV/c

The Theta(+) pentaquark baryon was searched for via the pi(-) p -> K- X reaction with a missing mass resolution of 1.4 MeV/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 1.92 GeV/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 degrees to 15 degrees in the laboratory frame is obtained to be 0.26 mu b/sr in the mass region of 1.51-1.55 GeV/c(2). The upper limit of the Theta(+) decay width is obtained to be 0.72 and 3.1 MeV for J(Theta)(P) = 1/2(+) and J(Theta)(P) = 1/2(-), respectively, using the effective Lagrangian approach.