CMB polarisation results from QUIET

Ingunn Kathrine Wehus23rd Rencontres de Blois, 1/6 -11

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

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

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

QUIET collaboration

Miami

Chicago (KICP)Fermilab

ColumbiaPrinceton

ManchesterOxford Oslo MPIfR-Bonn

KEK

Observational Site Atacama, Chile

5 countries, 13 institutes, ~30 people5 countries, 13 institutes, ~30 people

CaltechJPL

Stanford(KIPAC)

QUIET collaboration

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

QUIET Patches

Observing hours

Patch 2a 905

Patch 4a 703

Patch 6a 837

Patch 7b 223

All CMB 2668

Patch Gb 311In total 3458 observation hours

(77% cmb, 12% galaxy, 7% calib, 4% cut)Patch Gc 92

Q-band observing hours

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

Temperature maps – galactic centerQUIET vs WMAP

CMB temperature observations

QUIET vs WMAP – galactic center

Stokes Q Stokes U

QUIET vs WMAP – galactic plane

Stokes Q Stokes U

QUIET vs WMAP – CMB patch

Stokes Q Stokes U

Decomposition into E and B modes

The EE power spectrum

The BB power spectrum

• ML: r = 0.52+0.97−0.81.• PCL: r=0.35+1.06-0.87 (r < 2.2 at 95% confidence) (BICEP: r < 0.72 at 95% confidence)

Tensor-to-scalar ratio r

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

W-band galactic center

Stokes Q Stokes U

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

Current Performance(noise, duty cycle, 1/f) Likely Improvements

0.018r 0.00510 lensing 35

Phase II power spectra forecasts

Courtesy K. Smith

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

QUIET

• First Q-band results: arXiv:1012.3191• See http://quiet.uchicago.edu/ for more information