Spider Optimization II: Optical, Magnetic and Foreground Effects

TL;DR

Spider is a balloon-borne CMB polarization experiment aiming to detect primordial gravitational waves, with detailed simulations showing systematic and foreground effects are manageable for its scientific objectives.

Contribution

This work advances the analysis of systematic errors and foreground contamination in the Spider experiment through detailed simulations and modeling.

Findings

Systematic errors are controlled below the threshold for detecting r > 0.03.

Foreground contamination is sufficiently low for the experiment's goals.

Instrumental effects like beam mismatches are manageable with current design.

Abstract

Spider is a balloon-borne instrument designed to map the polarization of the cosmic microwave background (CMB) with degree-scale resolution over a large fraction of the sky. Spider's main goal is to measure the amplitude of primordial gravitational waves through their imprint on the polarization of the CMB if the tensor-to-scalar ratio, r, is greater than 0.03. To achieve this goal, instrumental systematic errors must be controlled with unprecedented accuracy. Here, we build on previous work to use simulations of Spider observations to examine the impact of several systematic effects that have been characterized through testing and modeling of various instrument components. In particular, we investigate the impact of the non-ideal spectral response of the half-wave plates, coupling between focal plane components and the Earth's magnetic field, and beam mismatches and asymmetries. We also present a model of diffuse polarized foreground emission based on a three-dimensional model of the Galactic magnetic field and dust, and study the interaction of this foreground emission with our observation strategy and instrumental effects. We find that the expected level of foreground and systematic contamination is sufficiently low for Spider to achieve its science goals.