2020 Fiscal Year Annual Research Report
Enhancing the direct search for dark matter in the XENON nT experiment with a water Cerenkov neutron detector
| Project/Area Number |
19H00675
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| Research Institution | The University of Tokyo |
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Principal Investigator |
MARTENS Kai 東京大学, カブリ数物連携宇宙研究機構, 准教授 (20535025)
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| Co-Investigator(Kenkyū-buntansha) |
竹田 敦 東京大学, 宇宙線研究所, 准教授 (40401286)
伊藤 好孝 名古屋大学, 宇宙地球環境研究所, 教授 (50272521)
身内 賢太朗 神戸大学, 理学研究科, 准教授 (80362440)
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| Project Period (FY) |
2019-04-01 – 2023-03-31
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| Keywords | neutron veto / water Cherenkov / gadolinium |
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| Outline of Annual Research Achievements |
Despite COVID-19 related restrictions great progress was made towards starting the XENONnT experiment at LNGS in Italy. The liquid xenon time projection chamber was filled with liquid xenon, and its water Cherenkov muon detector shield and the neutron veto were filled with pure water. Commissioning of the full XENONnT detector started in this configuration at the end of FY2020.
In January and February PI Kai Martens worked onsite at LNGS with our European colleagues to commission the neutron veto: All photomultiplier tube signals and FADC channels were checked and debugged with the help of the neutron veto's LED calibration system. After this pulser driven LED calibration system itself was brought into operation and tuned, a preliminary nVeto calibration with 2.6 MeV gamma rays from 208Tl was performed with a 232Th source; the results align with our expectations and projections for the neutron veto efficiency.
The main purpose of PI Kai Martens's trip were onsite preparations for the installation of the Kamioka technology based gadolinium water purification system in the summer of 2021; these onsite preparations were successfully concluded and we expect the installation to proceed without delay this summer.
Our Japanese group also got involved with the analysis of XENON1T data, and two of our senior members were elected to serve on the XENON collaboration's editorial board; please see the list of publications with neutron veto member authorship later in this report.
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| Current Status of Research Progress |
Current Status of Research Progress
3: Progress in research has been slightly delayed.
Reason
We originally expected to install the gadolinium water purification system in FY2020; this however was neither possible nor necessary as the COVID-19 pandemic delayed the implementation schedule for the whole experiment. As of this writing the Kamioka technology based gadolinium water purification system has left the the manufacturer's company and is in transit to LNGS, where our team will install the system at the experiment this summer. We will then proceed with gadolinium loading as the overall schedule for the experiment demands; the delay in the systems delivery and installation at LNGS does not adversely affect the XENONnT schedule for dissolving gadolinium in the neutron veto's water to bring the neutron veto to full efficiency.
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| Strategy for Future Research Activity |
In the summer of 2021 we will fully install the gadolinium water purification system at LNGS and commission it with pure water. With both the necessary amount of gadolinium sulfate octahydrate and the equipment to load it into the gadolinium water purification system already on site at LNGS and ready to be deployed we will wait with gadolinium loading until the whole detector is fully commissioned and the collaboration as a whole agrees to proceed with this irreversible step. Until then the neutron veto will have to rely on neutron capture on hydrogen in the water, and its overall efficiency will thus remain limited, but calibration procedures and Monte Carlo verification on it will proceed nonetheless to reach full efficiency and optimize science output as soon as possible.
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