1. Observational Cosmology Lab University of Wisconsin-Madison
Cosmic Microwave Background polarization observations with the POLAR and COMPASS experiments
Christopher O’Dell
Observational Cosmology Lab University of Wisconsin-Madison

2. TALK OUTLINE
CMB Introduction
CMB Polarization Description/Motivation
POLAR: Experiment/Analysis/Results
COMPASS and Future Prospects

3. Cosmic Microwave Background: 3 Characteristics
2. Spatial Anisotropy
T = K
Tcmb = K +/ mK
1. Spectrum
T ~ 20 K

4. Cosmological Theories Anisotropy Data in 2001
Church, Jaffe, & Knox 2001 astro-ph/

5. Cosmological Parameters in 2001

6. 3rd CMB Characteristic: Polarization
At last scattering, a quadrupole in temperature
anisotropy generates a polarized CMB signal.

7. Rotation of Coordinates by angle a
POLARIZATION MATH
Stokes’ Parameters
Intensity
Linear Polarization
Circular Polarization
Rotation of Coordinates by angle a

8. The E-B Decomposition Gradient-Type (E) : Symmetric Under Rotation
Symmetric Under Parity
Curl-Type (B):
Symmetric Under Rotation
Anti-symmetric Under Parity
Power Spectra:
TT : Anisotropy
EE : E-type Polarization
BB : B-type Polarization
TE : Temp-Epol Cross Correlation
Zaldarriaga & Seljak, 1998

9. Hu & Dodelson (Annual Reviews 2002)
The Four CMB Power Spectra TT TE
Hu & Dodelson (Annual Reviews 2002)

10. Why Measure CMB Polarization??
Is a fundamental prediction of the standard cosmological model.
Helps break degeneracies in determining fundamental cosmological parameters.
Probes Reionization History of the Universe.
B-modes are directly sensitive to primordial gravitational waves; the amplitude of the BB spectrum is proportional to the square root of the energy scale of inflation. They also help characterize the tensor-to-scalar ratio, r.
Polarization is required to truly test adiabaticity of the primordial seeds of structure. Parameter estimation is seriously degraded when a mixture of initial fluctuation types is allowed.
We often see something new and unexpected with each new window on the universe!

11. No Reionization.
Prms ~ 0.5 K
Zaldarriaga, 2001

12. Reionization at z ~ 30 Prms ~ 3.2 K t = 0.3 , Zre ~ 30
Zaldarriaga, 2001

13. 1965
1979
1983
1995
Zre ~ 30
Reionization Peak
Josh Gundersen, 2001

14. Polarization Observations of Large Angular Regions (POLAR)
A. de Oliveira-Costa (UPenn)
J. Gundersen (Miami)
B. Keating (Caltech)
S. Klawikowski (UW-Madison)
C. O’Dell (UW-Madison)
L. Piccirillo (Cardiff)
N. Stebor (UW-Madison)
D. Swetz (UW-Madison)
M. Tegmark (UPenn)
P. Timbie (UW-Madison)

15. The Spinning Correlation Polarimeterx y
CMB 
Ground Screens Ex Ey
OMT Gx Gy
0°, 180° Phase Shifter
Multiplier

16. POLAR Main Features
Clean, simple design: no lenses or mirrors no magnetic or moving parts (excepting overall rotation)
Corrugated conical feed horn achieves 7° beam with very low sidelobes.
HEMT amplifiers (25 K noise temperature, NET ~ 800 K • sec-1/2)
Commercial Cryocooler (no liquid cryogens).
Frequency bands: GHz, 3 sub-bands (plus basic sensitivity to Ix and Iy ).

20. Outer Ground Shield
Clam-Shell Dome
Clam-Shell Dome
Inner Ground Shield
20 K Dewar

21. Q and U at ~ 20 pixels on the sky, on a 7° ring at declination 43°
POLAR Scan Strategy
Q and U at ~ 20 pixels on the sky, on a 7° ring at declination 43°

22. Atmospheric Emission at Sea Level
H2O O2
Broad Line Emission
Unpolarized in absence of external fields
Possible O2 Zeeman splitting by earth’s B-field
Negligible
Will add to system noise, and affect required integration time.

23. Stability and Sensitivity

24. Polarized Foregrounds Power Spectra
(30%)
(3%)
Josh Gundersen, 1999

25. from Pine Bluff, Wisconsin
Observations and Data Selection
March 1st – May 31st, 2000
from Pine Bluff, Wisconsin

26. Mapmaking Data Vector True Sky Map Noise Vector Pointing Matrix
Problem : Re-construct the map from your data that is closest to the true, underlying map.
Solution : “Minimum Variance Mapmaking”
(not simply weighted averaging in the presence of 1/f noise)

28. Multi-Frequency Maps

29. Flat Band-Power Model :
E, B Spectra have constant power at all scales, characterized by variances : (TE2 , TB2)
Full 2D Likelihood:
Prior Constraint that TB = 0

30. Modern Polarization Upper Limits and POLAR band-powers
0.1
105
Modern Polarization Upper Limits and POLAR band-powers
104
103
E-Mode Limits
B-Mode Limits
100
PIQUE
CBI
ATCA 10
POLAR
1.0
0.1 10
100
1000

31. Onward! -> COMPASS UW-Madison UCSB Cardiff
UC-Davis Caltech Rome III
U-Miami

32. CMB Polarization: Full Speed Ahead!
Experiment Date Total Sensitivity l-range
DASI (HEMTs) Full Year ~ 1 uK
MAXIPOL (Spiderwebs) Mid May ~ 2 uK
B2.002K (PSBs) December < 1 uK
CBI (HEMTs) Full Year ~ 1 uK ?
MAP (HEMTs) Ongoing (data ~ 1yr?) ???
QUEST, BICEP, SPORT, ROPE, CAPMAP, etc.
???
PLANCK (HEMT/PSB) 2007? < 0.1 uK