Search for Pentaquark Θ+ in Hadronic Reaction at J-PARC

The first experiment at the J-PARC hadron facility, the J-PARC E19 experiment, aims at searching for the Θ + pentaquark in the hadronic reaction π − p → K − X using the missing-mass technique. Based on a superconducting magnet excited at 2.5 T, the spectrometer achieved the high mass resolution of 1.4 MeV/c2 for the Θ + production process. The first data taking was performed in the autumn of 2010. No significant structure was observed in the missing-mass spectrum. The upper limit obtained for the differential cross section is 0.26 μb/sr in the laboratory frame at a 90 % CL.