AI 中文总结
该研究针对BICEP阵列2026年远场波束测绘 campaign，表征150GHz及220/270GHz偏振计波束，推导差分参数、计算波束窗函数、验证反投影程序，还改进了噪声量化与增益校准的 pipeline。
AI 中文摘要
BICEP阵列（BA）是BICEP系列的当代仪器，为位于南极的小口径同轴折射望远镜，旨在通过对宇宙微波背景（CMB）的度尺度B模式偏振测量来约束张标比r。随着BA向更深灵敏度推进，仪器系统误差的控制，尤其是共置正交偏振探测器之间的波束形状失配，已成为将原始灵敏度转化为对r的可靠约束的愈发重要的因素。在本文中，我们报告2026年远场波束测绘（FFBM） campaign，该 campaign 使用热斩波源对BA2（150GHz）和BA3（220/270GHz）的波束进行表征。我们对每个探测器的波束拟合二维椭圆高斯函数，推导每对探测器的差分参数（差分指向、波束宽度和椭圆度）。所得高信噪比阵列平均波束图用于计算功率谱分析所需的波束窗函数Bl，而单个探测器波束则用于专用的波束卷积模拟，以验证温度到偏振（T→P）的反投影程序。在校正斩波孔径后，恢复的波束宽度遵循预期的λ/D排序。我们还描述了2026年 campaign 期间进行的两项 pipeline 改进：用于噪声量化的往返 jackknife 方法，以及基于elnod的增益校准。
英文摘要
BICEP Array (BA) is the current-generation instrument in the BICEP series of small-aperture, on-axis refracting telescopes at the South Pole, designed to constrain the tensor-to-scalar ratio $r$ through degree-scale measurements of B-mode polarization in the cosmic microwave background (CMB). As BA pushes to deeper sensitivity, control of instrumental systematics, and beam shape mismatch between the co-located orthogonally polarized detectors in particular, has become an increasingly important factor in translating raw sensitivity into a robust constraint on $r$. In these proceedings we report on the 2026 far field beam mapping (FFBM) campaign, which used a thermal chopped source to characterize the BA2 (150~GHz) and BA3 (220/270~GHz) beams. We fit two-dimensional elliptical Gaussians to each detector's beam, derive per-pair differential parameters (differential pointing, beamwidth, and ellipticity). The resulting high-signal-to-noise array-averaged beam maps are used to compute the beam window function $B_l$ for the power spectrum analysis, while the individual per-detector beams feed dedicated beam convolution simulations used to validate the temperature-to-polarization (T$\rightarrow$ P) deprojection procedure. After correcting for the chopper aperture, the recovered beamwidths follow the expected $λ/D$ ordering. We also describe two pipeline improvements carried out during the 2026 campaign: an out-and-back jackknife for noise quantification and an elnod-based gain calibration.
Comments10 pages, 8 figures, submitted to Proc. SPIE
