High-rate Performance of a Time Projection Chamber for an H-dibaryon Search Experiment at J-PARC

We have developed a gas electron multiplier (GEM)-based time projection chamber (TPC) for the H-dibaryon search experiment at J-PARC. High-rate K- beam particles enter a TPC gas volume of approximately 0.2 m(3), in a direction perpendicular to the electric field. A long-rectangular hollow section is located inside the TPC volume to accommodate a diamond target. We commissioned the TPC using 230-MeV protons with beam rates of up to 1 MHz. The TPC data acquisition system collected 5768 pad signals in full readout mode, with almost 100% efficiency, at a preset trigger rate of 230 Hz. We operated the TPC in an Ar/CH4 gas mixture (90/10) without a magnetic field. The spatial resolutions on the pad plane are measured to be 400-700 mu m, which correspond to 230-300 mu m in a magnetic field of 1 T. We confirmed high tracking capability at beam rates of up to 1 MHz.