J-PARC E19 Experiment: Pentaquark Θ+ Search in Hadronic Reaction at J-PARC

A search for the Θ^+ pentaquark in the $\pi ^{ - }p \to K^{ - }X$ reaction was performed at the J-PARC Hadron Facility. Two data samples were collected in 2010 and 2012 at π beam momenta of 1.92 and 2.0 GeV/c, respectively. No peak structure was observed in the missing mass spectra obtained from either data set. The upper limit for the production cross section averaged over the scattering-angle range of 2° to 15° in the laboratory frame was found to be 0.28 µb/sr. The decay width of the Θ^+ can be directly connected to the production cross section through a theoretical calculation using an effective Lagrangian. The estimated upper limits of the width were 0.41 and 2.8 MeV for the spin-parities of 1/2^+ and 1/2^−, respectively