Large Angular Scale Polarization Survey of the Cosmic Microwave Background - Phase Two

该奖项支持宇宙学大角度尺度探测器（CLASS）的新观测。CLASS的主要科学目标是（1）测量第一颗恒星何时照亮宇宙，（2）探测和描述宇宙开始时产生的原始引力波。第一个目标对于理解星系是如何形成的很重要，也提高了我们测量称为中微子的基本粒子质量的能力，对中微子的研究是物理学的前沿。第二个目标将告诉我们宇宙最早的时刻发生了什么，并将引力与量子力学联系起来，这是物理学的长期探索。为了实现这些目标，在过去十年中，已经开发了具有新技术的望远镜，并将其部署在智利阿塔卡马沙漠的安第斯山脉的高处。这是观测宇宙微波背景辐射（CMB）的首要地点，CMB是热早期宇宙的余辉。CLASS探测CMB偏振中最大角度尺度（超过10度）的变化，以达到其科学目标。更广泛的社会影响包括在美国和智利对学生和博士后进行严格的培训。CLASS通过大学和当地学校的公共活动、Quarknet高中教师培训和高中宇宙学模块的开发来接触公众。出版物和数据将公开分发。关于早期宇宙的转换数据将引起物理学家、天文学家、学生和公众的极大兴趣。CLASS在当前的CMB调查中是独一无二的，它将CMB偏振对应于角多极子，直到2阶。在这些尺度下，电离的星系际介质（再电离后）对CMB光子的散射改变了CMB的偏振角谱（E和B模式）。这种独特的低辐射特征的角功率谱是有针对性的CLASS测量光学深度再电离的宇宙方差限制和张量标量比在0.01水平。CLASS使用四台望远镜测量70%天空的CMB偏振。望远镜阵列在四个微波频率（40，90，150和220 GHz）下进行观测，以区分CMB信号和来自银河系的微波辐射。通过降低低频噪声实现低频测量的关键技术是利用可变延迟偏振调制器进行快速偏振幅度调制。其他技术开发包括新型微波光学器件、低温过渡边缘传感器和定制的高性能数据管道。最初的5年CLASS调查（由以前的MSIP资助）于2016年开始。该基金使该团队能够利用前五年在仪器、调查策略和数据分析管道方面的发展，并作为未来增强测量的桥梁。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award supports new observations with the Cosmology Large Angular Scale Surveyor (CLASS). The main science goals of CLASS are (1) to measure when the first stars lit up the universe and (2) to detect and characterize primordial gravitational waves created at the start of the universe. The first goal is important for understanding how galaxies formed and also improves our ability to measure the mass of fundamental particles called neutrinos, the study of which is a frontier in physics. The second goal will tell us what happened at the earliest moments of the universe and connects gravity with quantum mechanics, a long-term quest in physics. To accomplish these goals, telescopes with new technologies have been developed over the past decade and deployed high in the Chilean Andes, in the Atacama Desert. This is a premier site for observations of the Cosmic Microwave Background (CMB), which is the afterglow of the hot early universe. CLASS probes the largest-angular-scale (more than 10 degrees across the sky) variations in the CMB polarization to reach its science goals. Broader societal impacts include rigorous training of students and postdocs in the US and Chile. CLASS reaches the public through public events at universities and local schools, Quarknet high-school teacher training, and development of high-school-level cosmology modules. Publications and data will be publicly distributed. Transformational data on the early universe will be of enormous interest to physicists, astronomers, students, and the general public.CLASS is unique among current CMB surveys in targeting CMB polarization corresponding to angular multipoles down to ell of order 2. At these scales, scattering of CMB photons by the ionized intergalactic medium (post reionization) alters the CMB polarization angular spectra (both E and B-modes). This distinctive low-ell signature in the angular power spectrum is targeted by CLASS to measure the optical depth to reionization at the cosmic-variance limit and the tensor-to-scalar ratio at the 0.01 level. CLASS uses four telescopes to measure the CMB polarization over 70% of the sky. The telescope array observes at four microwave frequencies (40, 90, 150, and 220 GHz) to differentiate between the CMB signal and the microwave emission from our Galaxy. The key technology enabling the low-ell measurement through low-frequency noise reduction is rapid polarization amplitude modulation with a Variable-delay Polarization Modulator. Additional technology developments include novel microwave optics, cryogenic transition-edge sensors, and a custom high-performance data pipeline. The initial 5-year CLASS survey (funded under a previous MSIP), was begun in 2016. This grant allows the team to capitalize on developments in instrumentation, survey strategy, and data analysis pipeline from the first five years, and acts as a bridge to future, enhanced measurements.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.