NEWS-G Search for Light Dark Matter with Spherical Proportional Counters

NEWS-G 用球形正比计数器搜索光暗物质

• 批准号: SAPPJ-2020-00033
• 负责人: Giroux, Guillaume
• 金额: $ 18.21万
• 依托单位: Queen's University
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Project
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=763247
• 关键词: NEWS; Search; Light; Dark; Matter

Despite the overwhelming amount of astronomical and cosmological evidences for dark matter in the universe, its unknown nature is arguably the most pressing question of modern physics. WIMPs (Weakly Interacting Massive Particles) are a class of candidates emerging from beyond-the-Standard-Model frameworks that have been favoured so far. The 10 GeV to 10 TeV-mass WIMPs predicted by many well-motivated SUSY (supersymmetric) models have so far not been found by dark matter search experiments. This, combined with the lack of evidence for SUSY at the LHC (Large Hadron Collider), warrants for the extension of the search to lower WIMP masses. The motivation for this search is further strengthened by new theories predicting low-mass WIMPs such as asymmetric dark matter and dark sectors. The aim of the NEWS-G (New Experiment With Spheres - Gas) collaboration is the discovery of low-mass dark matter particles (< 1 GeV) using ultra-low background spherical proportional counters (SPC). SPCs are spherical gaseous detectors operated in proportional mode. A small sensor, held at high voltage at the centre of a grounded spherical shell, is drifting the primary ionization created by the interaction of a particle with the gaseous target. As the free charge approaches the sensor, the electric field becomes large enough to create an avalanche process. Sensitivity to single electrons, corresponding to an energy threshold of a few 10's of eV, is made possible by the high amplification gain and low intrinsic capacitance of the sensor. This, combined with the use of light target gases such as hydrogen, helium and neon which allows for the optimization of momentum transfer with low-mass WIMPs, makes the SPC a powerful tool in the search for WIMPs with masses below 1 GeV. The NEWS-G collaboration is comprised of 43 scientists from 11 institutions in Canada (Queen's University, SNOLAB/Laurentian University, TRIUMF, University of Alberta), France (LSM, CEA IRFU, LPSC Grenoble), Greece (Aristotle University of Thessaloniki), United Kingdom (University of Birmingham) and USA (PNNL). WIMP search results were recently reported by the collaboration using SEDINE, a 60-cm diameter prototype SPC installed at the Laboratoire Souterrain de Modane (LSM) in France. These results demonstrate the SPC operation at low energy threshold with a neon-methane mixture and at the time of publication were giving the most stringent limits on the WIMP-nucleus spin-independent cross-section for WIMP masses below 0.6 GeV. The competitive results obtained with SEDINE are promising for the next phase of the NEWS-G experiment: a 140-cm diameter SPC to be installed at SNOLAB in early 2020. Thanks to enhanced background control, sensor development and novel detector monitoring techniques, NEWS-G at SNOLAB is set to improve its sensitivity by a factor 1000 and is poised to obtain the world's best sensitivity to WIMP masses below 1 GeV.

尽管有大量的天文学和宇宙学证据证明暗物质存在于宇宙中，但其未知的性质可以说是现代物理学最紧迫的问题。WIMP（弱相互作用大质量粒子）是一类从超越标准模型框架中出现的候选粒子，迄今为止一直受到青睐。许多超对称（SUSY）模型预测的10 GeV到10 TeV质量的WIMP到目前为止还没有被暗物质搜索实验发现。这一点，再加上在大型强子对撞机（LHC）上缺乏超对称性的证据，保证了对更低WIMP质量的搜索的扩展。新的理论预测低质量WIMP，如不对称暗物质和暗扇区，进一步加强了这种搜索的动机。 NEWS-G（New Experiment With Spheres - Gas）合作的目的是使用超低背景球形正比计数器（SPC）发现低质量暗物质粒子（< 1 GeV）。SPC是以比例模式操作的球形气体检测器。一个小型传感器，在接地球壳的中心保持高电压，正在漂移粒子与气态目标相互作用产生的初级电离。当自由电荷接近传感器时，电场变得足够大以产生雪崩过程。通过传感器的高放大增益和低本征电容，对单个电子的灵敏度（对应于几十eV的能量阈值）成为可能。这一点，结合使用轻目标气体，如氢，氦和氖，允许优化的动量转移与低质量的WIMP，使SPC的一个强大的工具，在寻找质量低于1 GeV的WIMP。NEWS-G合作由来自加拿大（女王大学、SNOLAB/劳伦特大学、TRIUMF、阿尔伯塔大学）、法国（LSM、CEA IRFU、LPSC格勒诺布尔）、希腊（塞萨洛尼基亚里士多德大学）、联合王国（伯明翰大学）和美国（PNNL）11个机构的43名科学家组成。WIMP搜索结果最近由使用SEDINE的合作报告，SEDINE是一个直径60厘米的原型SPC，安装在法国的Modane的Souterrain（LSM）。这些结果表明，SPC操作在低能量阈值与氘-甲烷混合物，并在出版时给出了最严格的限制的WIMP核自旋无关的横截面的WIMP质量低于0.6 GeV。SEDINE获得的竞争结果对NEWS-G实验的下一阶段充满希望：将于2020年初在SNOLAB安装直径140厘米的SPC。得益于增强的背景控制、传感器开发和新型探测器监测技术，SNOLAB的NEWS-G将其灵敏度提高1000倍，并有望获得世界上对低于1 GeV的WIMP质量的最佳灵敏度。