Forecasts of effects of beam systematics and deprojection on the third-generation ground-based cosmic microwave background experiment

TL;DR

This paper evaluates how deprojection techniques can mitigate beam systematics in third-generation ground-based CMB experiments, ensuring accurate measurements of polarization and lensing without bias.

Contribution

It demonstrates that deprojection effectively removes beam mismatch systematics, preserving the integrity of CMB polarization and lensing measurements in the S3 experiment.

Findings

Deprojection recovers input power spectra accurately.

Residual systematics do not bias key CMB measurements.

Methods effectively mitigate beam mismatch effects.

Abstract

The ground-based cosmic microwave background (CMB) experiments are susceptible to various instrumental errors, especially for $B$-mode measurements. The difference between the response of two polarized detectors, referred to as the beam mismatch, would induce a $T\rightarrow P$ leakage when the detector pair is differenced to cancel the unpolarized signal. We applied the deprojection technique on the time-ordered mock data to mitigate the systematic contamination caused by beam mismatches by assuming the third-generation ground-based CMB experiment (S3). Our results show that the deprojection effectively recovered the input power spectra. We adopted the Needlet ILC (NILC) and constrained ILC (cILC) methods to reconstruct the foreground-cleaned $TEB$ maps, and we evaluated the level of residual systematic errors after the foreground cleaning pipeline by comparing the power spectra between the systematics-added data after deprojection and the systematics-free data. The results show that the residual beam systematics cleaned by deprojection do not bias the CMB measurements of the $T$, $E$, and $B$ modes nor the CMB lensing reconstruction or the estimation of the tensor-to-scalar ratio under the S3 sensitivity.