Polarization pursuers’ guide

We calculate the detectability of the polarization of the cosmic microwave background ~CMB! as a function of the sky coverage, angular resolution, and instrumental sensitivity for a hypothetical experiment. We consider the gradient component of the polarization from density perturbations ~scalar modes! and the curl component from gravitational waves ~tensor modes!. We show that the amplitude ~and thus the detectability! of the polarization from density perturbations is roughly the same in any model as long as the model fits the big-bang-nucleosynthesis ~BBN! baryon density and degree-scale anisotropy measurements. The degree-scale polarization is smaller ~and accordingly more difficult to detect! if the baryon density is higher. We show that the sensitivity to the polarization from density perturbations and gravitational waves is improved ~by a factor of 30! in a fixed-time experiment with a deeper survey of a smaller region of sky.