Search for H-dibaryon at J-PARC with a Large Acceptance TPC

¹ Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195, Japan
² Department of Physics, Pusan National University, Busan 609-735, Korea
³ Department of Physics and Astronomy, The University of New Mexico, Albuquerque, NM 87131-0001, USA
⁴ Department of Physics, Kyoto University, Kyoto 606-8502, Japan
⁵ Department of Physics, Florida International University, Miami, FL 33199, US A
⁶ Department of Physics and Astronomy, Ohio University, Athens, OH 45701, USA
⁷ Department of Physics, Tohoku University, Sendai, Miyagi 980-8578, Japan
⁸ Institute of Particle and Nuclear Studies (IPNS), High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
⁹ Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea
¹⁰ Faculty of Education, Gifu University, Gifu 501-1193, Japan
¹¹ Research Center for Nuclear Physics (RCNP), Osaka University, Ibaraki, Osaka 567-0047, Japan

^a e-mail: e-mail: hiroyuki.sako@j-parc.jp

Published online: 20 March 2014

Abstract

H-dibaryon has been predicted as a stable 6-quark color-singlet state. It has been searched for by many experiments but has never been discovered. Recent lattice QCD calculations predict H-dibaryon as a weakly bound or a resonant state close to the LL threshold. E224 and E522 experiments at KEK observed peaks in LL invariant mass spectra near the threshold in (K^-, K⁺) reactions, which were statistically not significant. Therefore, we proposed a new experiment E42 at J-PARC. It will measure decay products of ΛΛ and Λπ^-p in a (K^-, K⁺) reaction. We design a large acceptance spectrometer based on a Time Projection Chamber (TPC) immersed in a dipole magnetic field. The TPC surrounds a target to cover nearly 4π acceptance, and accepts K^- beams up to 10⁶ counts per second. To suppress drift field distortion at high beam rates, we adopt Gas Electron Multipliers (GEMs) for electron amplification and a gating grid. We show an overview of the experiment, the design of the spectrometer, and the R&D status of the TPC prototype.