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

该奖项支持宇宙大角尺度勘测者（CLASS）的新观测。CLASS的主要科学目标是(1)测量第一批恒星照亮宇宙的时间；(2)探测和表征宇宙起源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，也提高了我们测量被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在宇宙最初的时刻发生了什么，并将引力与量子力学联系起来，量子力学是物理学中的一个长期探索。为了实现这些目标，在过去的十年里，新技术的望远镜被开发出来，部署在智利安第斯山脉的高处，在阿塔卡马沙漠。这是观测宇宙微波背景（CMB）的首要地点，CMB是早期宇宙高温的余辉。CLASS探测CMB偏振的最大角度尺度（横跨天空超过10度）变化，以实现其科学目标。更广泛的社会影响包括在美国和智利严格培训学生和博士后。CLASS通过在大学和当地学校的公共活动、夸克网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。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，它针对的是CMB极化，对应于2阶的角多极子。在这些尺度上，电离星系间介质对CMB光子的散射（再电离后）改变了CMB偏振角光谱（E和b模式）。CLASS针对角功率谱中这种独特的低阱特征来测量宇宙方差极限下的光学再电离深度和0.01水平下的张量-标量比。CLASS使用四台望远镜测量70%天空上的CMB偏振。望远镜阵列在四个微波频率（40,90,150和220ghz）进行观测，以区分CMB信号和我们银河系的微波发射。利用变延时偏振调制器进行快速偏振调幅是实现低频降噪的关键技术。其他技术发展包括新型微波光学，低温过渡边缘传感器和定制高性能数据管道。最初的5年CLASS调查（由之前的MSIP资助）于2016年开始。这项拨款允许团队在前五年利用仪器、调查策略和数据分析管道的发展，并作为未来增强测量的桥梁。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识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.