Modeling optical systematics for the Taurus CMB experiment

TL;DR

This paper models various optical systematics for the Taurus balloon-borne CMB experiment to evaluate their impact on large-scale polarization measurements and develop mitigation strategies.

Contribution

It provides a comprehensive simulation of optical systematics for Taurus and assesses their effects on CMB polarization data, proposing calibration and design improvements.

Findings

Most HWP systematics can be mitigated with calibration and design choices.

Beam characterization is crucial to reduce dust contamination from far sidelobes.

Achromatic HWPs with five sapphire layers are preferred for systematic control.

Abstract

We simulate a variety of optical systematics for Taurus, a balloon-borne cosmic microwave background (CMB) polarisation experiment, to assess their impact on large-scale E-mode polarisation measurements and constraints of the optical depth to reionisation {\tau}. We model a one-month flight of Taurus from Wanaka, New Zealand aboard a super-pressure balloon (SPB). We simulate night-time scans of both the CMB and dust foregrounds in the 150GHz band, one of Taurus's four observing bands. We consider a variety of possible systematics that may affect Taurus's observations, including non-gaussian beams, pointing reconstruction error, and half-wave plate (HWP) non-idealities. For each of these, we evaluate the residual power in the difference between maps simulated with and without the systematic, and compare this to the expected signal level corresponding to Taurus's science goals. Our results indicate that most of the HWP-related systematics can be mitigated to be smaller than sample variance by calibrating with Planck's TT spectrum and using an achromatic HWP model, with a preference for five layers of sapphire to ensure good systematic control. However, additional beam characterization will be required to mitigate far-sidelobe pickup from dust on larger scales.