| 研究実績の概要 |
As the lightest hypernucleus, hypertriton serves as the corner stone for our understanding of hyperon-nucleon interaction. Recently, a much shorter lifetime by ~30% has been reported by several heavy-ion based experiments such as STAR and HypHI. This discrepancy was recognized as the hypertriton lifetime puzzle. With the support by this Kakenhi, we were able to propose an original experiment to measure the hypertriton lifetime at J-PARC with K-+He3-->Hypertriton+pi0 reaction.
The main innovation of our experiment is to identify the projectile pi0 meson by a fast Cherenkov based calorimeter made of PbF2 crystal. With the support of Kakenhi, we have constructed and commissioned the calorimeter with 40 pieces of 2.5x2.5x14cm PbF2 crystals with designed performance. We have also performed a feasibility study as the J-PARC T77 experiment with K-+He4-->H4_Lambda+pi0 reaction, which is almost identical with hypertriton lifetime measurement except the liquid He4 target instead of He3. In T77, we have successfully measured H4_Lambda hypernucleus lifetime with 10 times better signal to noise ratio than the previous KEK results. The remarkable performance of our novel experimental setup has been well recognized by the J-PARC Physics Advisory Committee as the establishment of a new experimental approach for the hypernucleus physics study.
Our proposal has been officially approved as the J-PARC E73 experiment and ready for the final data taking. Though depends on the J-PARC hadron beam schedule, we will have the first Physics data before this summer.
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