1. CMB polarisation results from QUIET
Ingunn Kathrine Wehus
23rd Rencontres de Blois, 1/6 -11

2. CMB polarisation
We can measure the polarisation of the CMB the same way as for light
The Stokes parameters quantify the polarization properties of a light ray
I = no filter at all
Q = linear polarizer at 0 and 90°
U = linear polarizer at -45 and 45 °
V = circular polarizer
I is just the temperature
Q and U combine to form E- and B-modes
No known physical process can generate V-polarised CMB radiation

3. B-modes and inflation
Stokes Q and U can be combined to E-modes and B-modes
Density fluctuations at last scattering produce E-modes
Gravitational lensing turns E-modes into B-modes at small scales
Primordial gravitational waves produce B-modes
Inflation predicts primordial gravitational waves
B-modes never measured
The tensor-to-scalar ratio r parametrizes how much B-modes there are compared to E-modes
r gives the energy scale of inflation

4. QUIET (Q/U Imaging ExperimenT)
QUIET is a groundbased experiment for measuring CMB polarisation
Constrains B-modes
Teaches us about inflation
Only B-mode radiometer experiment
Different, and possibly better, systematics
Unique radiometer on a chip technology
Input to case studies for the next generation satellite
Phase I (Pilot)
19 Q-band detectors (43 GHz) Aug 08 - May 09
91 W-band detectors (95 GHz) Jun 09 – Dec 10
Phase II (If funded)
~500 detectors in 3 bands (32, 44 and 90 GHz)
Measure the E- and B-mode spectra between l = 25 and 2500
detection of lensing at more than 20σ
constraining the tensor-to-scalar ratio r down to 0.01

5. QUIET collaboration

6. 5 countries, 13 institutes, ~30 people
QUIET collaboration
Manchester
Oxford
Chicago (KICP)
Fermilab
Oslo
MPIfR-Bonn
Stanford
(KIPAC)
KEK
Caltech
JPL
Columbia
Princeton
Observational Site
Atacama, Chile
Miami
5 countries, 13 institutes, ~30 people

7. The site
Located at 5080 m above sea level at the Chajnantor platau in the Atacama desert in Chile
One of the driest places on earth..
South pole has 40% lower PWV, but lower temperature results in comparable transmission
More of the sky is available than on south pole, and the same patch of sky can be observed from different angles. Good for systematics control
Accessible year round, day and night
..but still varying weather
Control room
Local inhabitants

8. QUIET Patches

9. Q-band observing hours
Patch 2a
905
Patch 4a
703
Patch 6a
837
Patch 7b
223
All CMB
2668
Patch Gb
311
In total 3458 observation hours
(77% cmb, 12% galaxy, 7% calib, 4% cut)
Patch Gc 92

10. Two independent pipelines
Pseudo-Cl (PCl) pipeline
Computationally less heavy; massive null-testing
Easy to simulate systematic errors
Maximum-likelihood (ML) pipeline
Produces optimally filtered map
Power spectrum calculated from exact likelihood
Needs the full covariance matrix from the previous step
Gives smaller and more accurate error bars

12. Temperature maps – galactic center QUIET vs WMAP

13. CMB temperature observations

14. QUIET vs WMAP – galactic center
Stokes Q Stokes U

15. QUIET vs WMAP – galactic plane
Stokes Q Stokes U

16. QUIET vs WMAP – CMB patch
Stokes Q Stokes U

17. Decomposition into E and B modes

18. The EE power spectrum

19. The BB power spectrum

20. Tensor-to-scalar ratio r
ML: r = −0.81.
PCL: r= (r < 2.2 at 95% confidence)
(BICEP: r < 0.72 at 95% confidence)

21. Future prospects More Q-band papers to follow:
Foregrounds, point sources, instrumentation, data analysis
W-band analysis now started
Optimized pipelines to handle more data
Null-testing ongoing

22. W-band galactic center
Stokes Q Stokes U

23. Future prospects More Q-band papers to follow:
Foregrounds, point sources, instrumentation, data analysis
W-band analysis now started
Optimized pipelines to handle more data
Null-testing ongoing
Future phase II plans
Improved detectors under development at JPL

24. Phase II power spectra forecasts
Current Performance
(noise, duty cycle, 1/f)
Likely Improvements
0.018r
10 lensing 
Courtesy K. Smith

25. Summary CMB polarisation is a future main source of cosmological data
Detecting primordial gravitational waves will teach us about inflation
QUIET is among the most sensitive CMB B-mode experiments in the world:
Unique radiometer technology
Q-band receiver is world leading in published array sensitivity at 69 uK sqrt(s)
Excellent location
Q-band results show that everything is working
Power spectra consistent with LCDM
Current constraint on tensor-to-scalar ratio is r = 0.35 ± 1.0
W-band results will be world leading when presented later this year
Phase II may possibly detect gravitational waves.
Will constrain r below 0.01

26. First Q-band results: arXiv:1012.3191
See for more information
QUIET