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تسجيل مستخدم جديدDevelopment of time projection chamber for precise neutron lifetime measurement using pulsed cold neutron beams
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A new time projection chamber (TPC) was developed for neutron lifetime measurement using a pulsed cold neutron spallation source at the Japan Proton Accelerator Research Complex (J-PARC). Managing considerable background events from natural sources and the beam radioactivity is a challenging aspect of this measurement. To overcome this problem, the developed TPC has unprecedented features such as the use of polyether-ether-ketone plates in the support structure and internal surfaces covered with $^6$Li-enriched tiles to absorb outlier neutrons. In this paper, the design and performance of the new TPC are reported in detail.
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A neutron decays into a proton, an electron, and an anti-neutrino through the beta-decay process. The decay lifetime ($sim$880 s) is an important parameter in the weak interaction. For example, the neutron lifetime is a parameter used to determine th
e |$V_{rm ud}$| parameter of the CKM quark mixing matrix. The lifetime is also one of the input parameters for the Big Bang Nucleosynthesis, which predicts light element synthesis in the early universe. However, experimental measurements of the neutron lifetime today are significantly different (8.4 s or 4.0$sigma$) depending on the methods. One is a bottle method measuring surviving neutron in the neutron storage bottle. The other is a beam method measuring neutron beam flux and neutron decay rate in the detector. There is a discussion that the discrepancy comes from unconsidered systematic error or undetectable decay mode, such as dark decay. A new type of beam experiment is performed at the BL05 MLF J-PARC. This experiment measured neutron flux and decay rate simultaneously with a time projection chamber using a pulsed neutron beam. We will present the world situation of neutron lifetime and the latest results at J-PARC.
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The neutron lifetime is one of the basic parameters in the weak interaction, and is used for predicting the light element abundance in the early universe. Our group developed a new setup to measure the lifetime with the goal precision of 0.1% at the
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