分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： ALETHEIA is a newly established dark matter direct detection project that aims at hunting for low-mass WIMPs. TPB is widely implemented in liquid helium and argon experiments to shift VUV photons to visible light. We first report that we have successfully coated $\sim 3 ~\mu$m TPB on the inner walls of a 10-cm cylindrical PTFE detector; we split the coating process into two steps to have all of the surfaces being coated with the same thickness; three independent methods were applied to figure out the thickness of the TPB coating layers, and consistent results were obtained. Second, with an SEM machine, we scanned the surface of TPB coating sample films exposed to different cryogenic temperatures. The first group of sample layers were immersed into a liquid nitrogen dewar for forty hours, the second group samples were cooled to 4.5 K for three hours, and the third group stayed at room temperature after coating. The SEM-scanned images of the sample films barely show any noticeable difference.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Junhui Liao
Yuanning Gao
Zhuo Liang
Zebang Ouyang
Zhaohua Peng
Xiuliang Zhao
Lei Zhang
Lifeng Zhang
Jian Zheng
Jiangfeng Zhou
摘要： No existence of convincing signals has become a ``new normal'' in the Dark Matter (DM) direct detection community for decades. Among other possibilities, the ``new normal'' might indicate that in addition to the traditional NR (Nuclear Recoil) events, ER (Electron Recoil) ones could also result from DM interactions, which have been considered as backgrounds historically. Further, we argue that ER and NR-like DM signals could co-exist in a detector's same dataset. So in total, there would be three scenarios we can search for DM candidate signals: (i) NR excess only, (ii) ER excess only, and (iii) both ER and NR excess. To effectively identify possible DM signals under the three scenarios, a DM detector should (a) have the minimum ER and NR backgrounds and (b) be capable of discriminating ER events from NR ones. Accordingly, we introduce the newly established project, ALETHEIA (A Liquid hElium Time projection cHambEr In dArk matter), which implements liquid helium TPCs (Time Projection Chamber) to hunt for low-mass ($\sim $100s MeV/c$^2$ - 10 GeV/c$^2$) DM. Presumably, the LHe TPC technology would have the minimum intrinsic backgrounds and strong ER/NR discrimination, therefore, be capable of identifying any kind of DM induced excess if it exists at all.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： ALETHEIA is a newly established dark matter direct detection project that aims at hunting for low-mass WIMPs. TPB is widely implemented in liquid helium and argon experiments to shift VUV photons to visible light. We first report that we have successfully coated $\sim 3 ~\mu$m TPB on the inner walls of a 10-cm cylindrical PTFE detector; we split the coating process into two steps to have all of the surfaces being coated with the same thickness; three independent methods were applied to figure out the thickness of the TPB coating layers, and consistent results were obtained. Second, with an SEM machine, we scanned the surface of TPB coating sample films exposed to different cryogenic temperatures. The first group of sample layers were immersed into a liquid nitrogen dewar for forty hours, the second group samples were cooled to 4.5 K for three hours, and the third group stayed at room temperature after coating. The SEM-scanned images of the sample films barely show any noticeable difference.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Junhui Liao
Yuanning Gao
Zhuo Liang
Zhaohua Peng
Zebang Ouyang
Lifeng Zhang
Lei Zhang
Jiangfeng Zhou
摘要： Dark Matter (DM) is one of the most critical questions to be understood and answered in fundamental physics today. Observations with varied astronomical and cosmological technologies already pinned down that DM exists in the Universe, the Milky Way, and the Solar System. However, the understanding of DM under the language of elementary physics is still in progress. DM direct detection aims to test the interactive cross-section between galactic DM particles and an underground detector's nucleons. Although Weakly Interactive Massive Particles (WIMPs) is the most discussed DM candidate, the null-WIMPs conclusion has been consistently addressed by most convincing experiments in the field. The low-mass WIMPs region (100s MeV/c$^2$ - 10 GeV/c$^2$) has not been fully exploited comparing to high-mass WIMPs (10 GeV/c$^2$ - 1 TeV/c$^2$) experiments which implement liquid xenon or argon TPCs (Time Projection Chambers). The ALETHEIA experiment aims to hunt for low-mass WIMPs with liquid helium-filled TPCs. In this paper, we go through the physics motivation of low-mass DM, the ALETHEIA detector's design, a series of R&D programs that should be launched to address a liquid helium TPC's functionality, and possible analysis channels available for DM searches. We designed and homemade a 30 g liquid helium prototype detector at CIAE. In Summer 2021, the detector was cooled down to 4.5 K successfully. The detector's dark current is less than ten pA for an external voltage up to 17 kV/cm when filled with vacuum, 1 atm nitrogen gas, and liquid nitrogen.
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