Solve the hypertriton lifetime puzzle

2018 Fiscal Year Annual Research Report

• Project/Area Number: 17H04842
• Research Institution: Institute of Physical and Chemical Research
• Principal Investigator: MA YUE 国立研究開発法人理化学研究所, 開拓研究本部, 専任研究員 (80639576)
• Project Period (FY): 2017-04-01 – 2021-03-31
• Keywords: Hypertriton / calorimeter / cryogenic target

Outline of Annual Research Achievements

In these two fiscal years, we were able to make a considerable progress even with unavoidable circumstances change including the delayed delivery of PbF2 crystal, short of crystal supply and corresponding modification of the original setup. As a result, we revised the original experimental setup by using less PbF2 crystals with the help of systematic Monte Carlo simulation study and optimization. The updated version of experimental proposal was submitted to J-PARC PAC for beam time evaluation and has been conditionally approved. The new version of experimental setup allocates the PbF2 crystal based calorimeter closer to the liquid He3,4 target in order to maintain the same acceptance as before but using less volume of the PbF2 detector materials. Correspondingly, the vacuum chamber for the liquid He3,4 target was also modified and adopt a much thiner design to avoid conflicting with the PbF2 calorimeter. In new the design of the cryogenic target system, we will employ mechanical cooling system with improved performance.
After fixing the revised experimental setup, we constructed the PbF2 calorimeter and tested its performance at ELPH, Tohoku University with positron beam up to 800 MeV in December 2019. The performance of the PbF2 calorimeter is comparable with our simulation and ready for the beam time. The new cryogenic system has also been successfully operated. By March of 2020, we have assembled the full setup at J-PARC K1.8 beam line and ready for the data taking with liquid He4 target as a feasibility test suggested by J-PARC PAC committee.

Current Status of Research Progress

3: Progress in research has been slightly delayed.

Reason

The delay happens mainly because of the reformulation of the PbF2 supplier as previously described. As the only supplier for the PbF2 crystal, the Shanghai Institute of Ceramics, China Academy of Sciences, undergoes a structural reformulation, which prohibits the direct contract between research group and external buyer like us. The new agent responsible for the purchasing process consumed much more time to understand the situation and caused the delayed delivery of the PbF2 crystals. It also took us some time to revise our original setup to accommodate the lack of PbF2 supply as expected. We don't foresee any further problem and an essential progress in the coming year can be expected.

Strategy for Future Research Activity

The revised proposal has been conditionally approved by J-PARC PAC and we will concentrate on the coming beam time with liquid He4 target. After clarify the feasibility study with He4 target, we will take physical data with He3 target for the hypertriton lifetime puzzle.