Development of a GEM-TPC for H-dibaryon search experiment at J-PARC

Sako, Hiroyuki   ; Ahn, J. K.*; Baek, K. H.*; Bassalleck, B.*; Fujioka, H.*; Guo, L.*; Hasegawa, Shoichi   ; Hicks, K.*; Honda, R.*; Hwang, S. H.*; Ichikawa, Yudai   ; Ieiri, Masaharu*; Imai, Kenichi; Kim, S. H.*; Kiuchi, Ryuta*; Lee, H. S.*; Nakazawa, K.*; Naruki, M.*; Ni, A.*; Niiyama, Masayuki*; Ozawa, K.*; Park, J. Y.*; Ryu, S. Y.*; Sato, Susumu  ; Shirotori, Kotaro*; Sugimura, Hitoshi; Sumihara, M.*; Tanida, Kiyoshi   ; Takahashi, H.*; Takahashi, T.*

A TPC has been developed for J-PARC E42 experiment to search for H-dibaryon in (, ) reaction. An event with 2 and 2 protons decaying from H-dibaryon is searched for inside the TPC. The TPC has octagonal prism shape drift volume with about 50 cm diameter with 55 cm drift length filled with Ar-CH (90:10) gas. At the end of the drift volume, 3-layer GEMs are equipped. In order to analyze momenta of produced particles, the TPC is applied with 1 T dipole magnetic field parallel to the drift electric field with a superconducting Helmholz magnet. In order to maximize the acceptance of H-dibaryon events, a diamond target is installed inside the TPC drift volume, in a cylindrical hole opened from the top to the middle of the drift volume. Since extremely high-rate beam is directly injected into the TPC drift volume to the target, a gating grid and GEMs are adopted to suppress positive-ion feedback.