A Projected Estimate of the Reionization Optical Depth Using the CLASS Experiments Sample-Variance Limited E-Mode Measurement

We analyze simulated maps of the Cosmology Large Angular Scale Surveyor (CLASS) experiment and recover a nearly cosmic-variance limited estimate of the reionization optical depth $tau$. We use a power spectrum-based likelihood to simultaneously clean foregrounds and estimate cosmological parameters in multipole space. Using software specifically designed to constrain $tau$, the amplitude of scalar fluctuations $A_s$, and the tensor-to-scalar ratio $r$, we demonstrate that the CLASS experiment will be able to estimate $tau$ within a factor of two of the full-sky cosmic variance limit allowed by cosmic microwave background polarization measurements. Additionally, we discuss the role of CLASSs $tau$ constraint in conjunction with gravitational lensing of the CMB on obtaining a $gtrsim4sigma$ measurement of the sum of the neutrino masses.