在以$^{3}$ He为缓冲气体的CAST实验中用Micromegas探测器搜索太阳轴子
Solar Axion search with Micromegas detectors in the CAST Experiment with $^{3}$He as buffer gas
摘要：
轴子是在SM的扩展中作为强CP问题的解决方案提出的动机良好的粒子。此外，还有类轴子粒子（ALP），它出现在SM的扩展中，并与轴子共享相同的现象学。轴子和ALP是解决暗物质问题的候选者。自2003年以来，欧洲核子研究中心的轴子太阳望远镜一直在寻找太阳轴子。CAST利用一个退役的LHC偶极磁铁，利用日光镜技术，太阳轴子可以重新转换为光子。在CAST运行的四个探测器中有三个是Micromegas型的。本文介绍了在2011年CAST数据采集活动期间对三个Micromegas探测器的数据进行的分析，得到了在95 $\%$的置信水平下，对于1到1.17 eV的轴子质量，g $_{a γ}$ < 3.90 $\times$ 10 $^{-10}$ GeV $^{-1}$的耦合常数的极限。CAST Micromegas探测器采用不同的策略来降低背景水平。此外，还开发了不同的测试台，以了解背景的起源。在CAST对Micromegas探测器的升级中显示了低背景技术的最新水平，这导致背景降低了$\sim$ 6倍。其转化为CAST灵敏度的改善，因子$\sim$ 2.5。除CAST外，还提出了新一代轴子日像仪：IAXO-国际轴子天文台。IAXO将通过利用CAST的所有奇异性来增强日光镜技术，这些奇异性被实施到大型超导环形磁体、专用X射线光学器件和超低背景探测器中。本文介绍了IAXO的设计方案，并对IAXO的灵敏度进行了研究。IAXO将超过CAST一个数量级以上，进入一个未探索的参数空间区域。
英文摘要：
Axions are well motivated particles proposed in an extension of the SM as a solution to the strong CP problem. Also, there is the category of Axion-Like Particles (ALPs) which appear in extensions of the SM and share the same phenomenology of the axion. Axions and ALPs are candidates to solve the Dark Matter problem. CAST, the CERN Axion Solar Telescope is looking for solar axions since 2003. CAST exploit the helioscope technique using a decommissioned LHC dipole magnet in which solar axions could be reconverted into photons. Three of the four detectors operating at CAST are of the Micromegas type. The analysis of the data of the three Micromegas detectors during the 2011 data taking campaign at CAST is presented in this thesis, obtaining a limit on the coupling constant of g$_{a γ}$ < 3.90 $\times$ 10$^{-10}$ GeV$^{-1}$ at a 95$\%$ of confidence level, for axion masses from 1 to 1.17 eV. CAST Micromegas detectors exploit different strategies developed for the reduction of the background level. Moreover, different test benches have been developed in order to understand the origin of the background. The state of art in low background techniques is shown in the upgrades of the Micromegas detectors at CAST, which has led to a reduction of the background in a factor $\sim$6. It translates in an improvement of the sensitivity of CAST in a factor $\sim$2.5. Beyond CAST a new generation axion helioscope has been proposed: IAXO-the International Axion Observatory. IAXO will enhance the helioscope technique by exploiting all the singularities of CAST implemented into a large superconducting toroidal magnet, dedicated X-ray optics and ultra-low background detectors. A description of the IAXO proposal and the study of the sensitivity of IAXO are presented in this thesis. IAXO will surpass CAST in more than one order of magnitude, entering into an unexplored parameter space area.
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