1. photo: Keith Vanderlinde Detection of tensor B-mode polarization : Why would we need any more data?

2. If the measured r angular-spectrum leads to any surprising physics, it is crucial to establish beyond any doubt that the signal originates in the CMB. There are not good enough templates for polarized synchrotron or polarized dust emission. Data would help. Direct r-detection at more wavelengths than two would help. The WMAP synchrotron template is dust-contaminated by the Bicep2 frequency.

3. Is the shape of the BB power spectrum unambiguously due to tensor- modes? Measurements with higher resolution in l will help. Detection of the re-ionization bump at l ~ 10 would be decisive. Good measurements of EE at higher angular frequencies can lead to calculation of the lensing conversion of EE to BB at all angular scales, and thus to a cleaner spectrum at the largest angular scales

4. Is the deficit in TT at large angular scales cosmic variance or a hint of new physics? Measuring EE and TE gives us access to more modes, which might reduce the ambiguity. Smith et al.

5. ACT (ACTpol, Advanced ACT, ABS) Bicep3 & Keck CLASS Ebex Piper Pixie Planck Polarbear South Pole Telescope (SPTpol, SPT3g,..) Spider There are a lot of CMB polarization experiments already under way or very far along.

6. BICEP1 (2006-2008) BICEP2 (2010-2012) Keck Array (2011-2016) BICEP3 (2015-2016)

7. KECK (spud) 2560 TES 5 cameras Two colours Data from 2012 & 2013 seasons in hand. 9.5  K rt s Now with two cameras at 95 GHz

8. CLASS: Four colour large angular scales To begin operation end of 2014.

9. CLASS will deploy a 40 GHz and a 90 GHz channel this year. The telescope scans 70% of the sky and is designed to explore the re-ionization peak.

10. Advanced ACTPol (AdvACT) Observations ~20,000 deg 2 survey with complete LSST overlap as well as DES, ALMA, and other observatories located in Chile 90 GHz and 150 GHz bolometers Substantial overlap with spectroscopic surveys (SDSS, PFS, DESI)

11. Polarization Modulation  Low l 11 ABS on-sky performance ABS HWP (33 cm dia, 1-layer sapphire, air bearings, run via air compressor) Kusaka et al, RSI 85, 024501, 2014

12. AdvACT: Power Spectra High S/N B-mode detections for r > 0.01 are measured in independent frequency bands (90 & 150 GHz) and on many patches across the sky. This provides important cross- checks on any detected signal Also shown: – Error bars before and after foreground cleaning – Varying amplitudes of the gravitational lensing signal for different values of the sum of the neutrino masses – Planck forecasts Error bars above shown for r = 0.2

13. Temperature spectrum (as before) E-mode polarization spectrum, scalar (blue) & tensor (red) terms B-mode polarization spectrum, tensor (red) & gravitational lensing (green) terms Predicted Polarization Signal, r=0.10 Observed=scalar+tensor Observed=tensor (+lensing)