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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 threshold. E224 and E522 experiments at KEK observed peaks in 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 and 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 4 acceptance, and accepts K - beams up to 10 6 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.
Highlights
The H-dibaryon has been predicted as the most stable color and SU(3)f single 6-quark state in 1977 [1]
It has the unique feature that the target is enclosed inside the drift volume to maximize the H-decay event acceptance, while an extremely high-rate K- beam must be directly injected to the drift volume
In order to cope with the high-rate beam, we adopted Gas Electron Multipliers (GEMs) and a gating grid
Summary
The H-dibaryon has been predicted as the most stable color and SU(3)f single 6-quark state (uuddss) in 1977 [1]. There were some indications of H-dibaryons in two experiments, E224 [3] and E522 [4] at KEK Proton Synchrotron They observed peaks near the threshold in invariant mass spectra. HAL QCD [6] and NPLQCD [7] collaborations extended these Lattice QCD calculations to the H-dibaryon studies. They calculated binding energies of H-dibaryon turned out to be 7.4±2.1±5.8 MeV (the errors are statistical and systematic) and -13±14 MeV (the error is statistical only) [6,7,8], respectively. We proposed a new experiment E42 at J-PARC [9] to have a two-order of magnitude higher statistics data sample than the KEK experiments
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