量化差分波束响应对2016至2024年BICEP宇宙微波背景偏振数据的系统影响
Quantifying the systematic impact of differential beam response on the BICEP CMB polarization data from 2016 through 2024
AI总结：
该研究针对2016-2024年BICEP CMB偏振数据，量化差分波束响应的系统影响，通过原位波束测量与模拟优化去投影方法，将BICEP3的等效r泄漏幅度降至(1.12±0.06)×10⁻³并计划扩展去投影基。
AI中文摘要：
随着包括BICEP3、BICEP Array及未来BICEP实验在内的宇宙微波背景（CMB）偏振实验为搜寻暴胀产生的原初B模式，不断获得更深的偏振图，将仪器系统误差限制在统计不确定性以下变得愈发具有挑战性。由于BICEP望远镜的偏振测量是通过对共置的正交偏振探测器进行成对差分实现的，差分波束响应会导致温度到偏振（T→P）的泄漏，对推断出的张量标量比r引入潜在的系统偏差。为缓解这种泄漏，最低阶的波束失配模式会通过去投影从CMB偏振图中滤除，但仍存在未去投影的残余模式。为量化这种残余污染，我们在南半球夏季校准活动期间对BICEP接收机进行了专门的原位远场波束测量。我们基于测量得到的每个探测器波束，通过一组专门的时序流模拟量化未去投影残余的系统影响。这些“波束测量驱动的模拟”得出了未去投影残余源生的虚假偏振信号的估计值。我们总结了与BK24数据发布相关的波束测量结果，并给出了95 GHz下BICEP3的初步残余泄漏结果。对于2016至2024年的BICEP3，将所有6个标准模板与读出串扰模板及其径向平滑对应项一起去投影，可将等效r泄漏幅度从ρ=(4.5±0.7)×10⁻³降低至(1.12±0.06)×10⁻³。我们还描述了一项正在进行的计划，该计划将基于将候选泄漏模式与物理仪器参数扰动关联的正向光学模型，把去投影基扩展到其历史6种模式之外。
英文摘要：
As cosmic microwave background (CMB) polarization experiments, including BICEP3, BICEP Array, and future BICEP experiments, achieve ever-deeper polarization maps in search of primordial B-modes sourced from inflation, constraining instrumental systematics below statistical uncertainties becomes progressively more challenging. Since polarimetry in the BICEP telescopes is performed by pair-differencing co-located, orthogonally polarized detectors, differential beam response leads to temperature-to-polarization ($T \rightarrow P$) leakage, introducing a potential systematic bias on the inferred tensor-to-scalar ratio $r$. To mitigate this leakage, the lowest-order beam mismatch modes are filtered out of the CMB polarization maps through deprojection; however, residual undeprojected modes remain. To quantify this residual contamination, we perform dedicated in situ far-field beam measurements of the BICEP receivers during austral-summer calibration campaigns. We quantify the systematic impact of the undeprojected residuals with a specialized set of timestream simulations based on the measured per-detector beams. These "beam measurement-informed simulations" yield an estimate of the false polarized signal sourced by the undeprojected residuals. We summarize the beam measurements relevant to the BK24 data release and present preliminary residual-leakage results for BICEP3 at 95 GHz. For BICEP3 over 2016-2024, deprojecting all six standard templates together with readout-crosstalk templates and their radially smoothed counterparts reduces the equivalent-$r$ leakage amplitude from $ρ=(4.5\pm0.7)\times10^{-3}$ to $(1.12\pm0.06)\times10^{-3}$. We further describe an ongoing program to extend the deprojection basis beyond its historical six modes, guided by a forward optical model that relates candidate leakage modes to perturbations of physical instrument parameters.
