Pentaquark search experiment at J-PARC

We have performed an experiment to search for pentaquark by hadron reaction at Hadron Experimental Facility of J-PARC. We attempted to measure the mass of pentaquark by mass defect method. With the reaction π^-p→K^- at 1.92 GeV/c², masses of incident π^- and scattered K^- were measured by a spectrometer with high momentum resolution. The experiment has not resulted in finding pentaquark and the upper limit of the differential cross section of production has been given to be 0.26 μb/sr(2° - 15°). The upper limits of decay width were obtained to be 0.72 MeV(J_Θ^P=1/2⁺) and 3.1 MeV(J_Θ^P=1/2^-) by using the value of upper limit of cross section and the theoretical calculation. Although the result of our experiment gives strong limitation for the production of pentaquark, it does not deny the results by other reaction processes. (J.P.N.)