Search for the Θ+ pentaquark at J-PARC

We have been searching for the Θ+ pentaquark via the π−p→K−X reaction at the J-PARC hadron facility. No peak structure was observed in the missing mass spectrum obtained at 1.92GeV/c beam momentum. The upper limit for the production cross section averaged over the scattering angle from 2° to 15° in the laboratory frame was derived to be 0.26μb/sr. In order to make a more stringent constraint we have also performed a measurement at 2.0GeV/c. Present analysis status of this new data is reported.