The “QUEST” for CMB Polarization

The “QUEST” for CMB The “QUEST” for CMB PolarizationPolarization

Walter K. GearWalter K. Gear

Cardiff UniversityCardiff University

Talk StructureTalk Structure

• CMB Review CMB Review

• Why Polarization ?Why Polarization ?

• The QUEST ExperimentThe QUEST Experiment

• (Future Plans)(Future Plans)

Curtesy Wayne Hu htp:\\background.uchicago.eduCurtesy Wayne Hu htp:\\background.uchicago.edu

CMB: Cosmic Rosetta Stone...CMB: Cosmic Rosetta Stone...

• CMB arises from last-scattering surface CMB arises from last-scattering surface ~300,000 years after the Big Bang~300,000 years after the Big Bang

• This is the earliest direct image of the This is the earliest direct image of the Universe we can ever obtain (EM Universe we can ever obtain (EM anyway…)anyway…)

• The imprints of structure of the Universe The imprints of structure of the Universe today AND BigBang/inflation should also today AND BigBang/inflation should also be imprinted there...be imprinted there...

Constraining InflationConstraining Inflation• Accurate measurement of the CMB

can constrain the nature of the inflationary potential

• in particular the ratio of scalar to tensor fluctuation amplitude r=T/S

• and the slope n of the assumed power-law spectrum P(k):

)ln(

)ln(1

kd

Pdn k

Scalars and TensorsScalars and Tensors

• Inflation predicts a mixture of scalar (pure Inflation predicts a mixture of scalar (pure density) and Tensor (gravity wave)fluctuationsdensity) and Tensor (gravity wave)fluctuations

• The precise ratio is a function of the type of The precise ratio is a function of the type of field which causes inflationfield which causes inflation

• Scalar fluctuations couple to matter and Scalar fluctuations couple to matter and provide the “seeds” for structure formationprovide the “seeds” for structure formation

• Tensor perturbation causes a ‘background’ of Tensor perturbation causes a ‘background’ of gravity wavesgravity waves

CMB: The Golden age….CMB: The Golden age….

Temperature power Temperature power spectraspectra

l

lm

Tlm

Tlm

Tl

mmllTl

Tml

Tlm

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CMB: The Golden Age …..CMB: The Golden Age …..

CMB: The Golden Age …..CMB: The Golden Age …..

Flat, n=1; b = 0.021, c = 0.196, Ho = 47; b = 0.022, c = 0.132, Ho = 68, = 2/3

The MAP Temperature The MAP Temperature results…..results…..

The anisotropy measurements The anisotropy measurements have been a triumph, BUT ….have been a triumph, BUT ….

• ““With temperature data With temperature data alone, alone, r of less than ~0.1 r of less than ~0.1 cannot be cannot be detected, no detected, no matter how matter how accurate the measurement” accurate the measurement”

(Kinney (Kinney 1999 astroph/98062591999 astroph/9806259))

• With polarization data With polarization data however however we can break this we can break this degeneracy degeneracy (amongst (amongst others)others)

The power of polarization…The power of polarization…• Fundamental prediction of standard theory, if not Fundamental prediction of standard theory, if not

detected at detected at then there would be real problem then there would be real problem

• The extra information provided by polarization The extra information provided by polarization allows much better constraints on some vital allows much better constraints on some vital cosmological parameters - 4 power spectra rather cosmological parameters - 4 power spectra rather than 1.than 1.

• Combination of P and Combination of P and T improves some T improves some parameter constraints by factors 2-3 in most models parameter constraints by factors 2-3 in most models

• Break degeneracy between intrinsic fluctuation Break degeneracy between intrinsic fluctuation amplitude and re-ionizationamplitude and re-ionization

• Separate scalar and tensor modes in the initial Separate scalar and tensor modes in the initial fluctuation spectra, if B as well as E modes can be fluctuation spectra, if B as well as E modes can be detecteddetected

Temperature is a scalar but Polarization is a Temperature is a scalar but Polarization is a second-rank Tensorsecond-rank Tensor

2) (

) ( ) () (

) ( ) (0

) (

) (

l

l

l mn B

lmY B

lma n E

lmY E

lma

T

n P

and

B E n PIt is convenient to write this is as the sum of the It is convenient to write this is as the sum of the gradient and curl of a scalar and vector field E and B gradient and curl of a scalar and vector field E and B

[but has [but has nothing nothing to do with E and B EM fields !!]to do with E and B EM fields !!]

E and B modesE and B modes

• The scalar function E The scalar function E represents pure density represents pure density fluctuationsfluctuations

• The tensor function B The tensor function B represents metric fluctuations - represents metric fluctuations - gravity wavesgravity waves

Polarisation of the CMBPolarisation of the CMB

Q U

+Temperature

• Generated by Thompson Generated by Thompson scattering off electrons in scattering off electrons in quadrupolar motion.quadrupolar motion.

PQU

PolarisationMatrix:

E/B DecompositionE/B Decomposition

• Can decompose Q,U into:Can decompose Q,U into:

– E-modes (even-parity):E-modes (even-parity):

– B-modes (odd-parity):B-modes (odd-parity):

• E-modes generated by scalar & tensor E-modes generated by scalar & tensor perturbations.perturbations.

• B-modes generated by tensors & grav. lensing.B-modes generated by tensors & grav. lensing.

B

E

B

E

Cold Spot Hot Spot

Pure E(left) & B(right)Pure E(left) & B(right)

CMB polarisation spectraCMB polarisation spectra• Have 4 possible spectra:Have 4 possible spectra: TT, TE, EE, BB.• TB = EB = 0 by parity.by parity.

GravitationalWaves

Reionisation

GravitationalLensing

SilkDamping

Sachs-Wolfe

Acoustic Oscillations

19/9/2002: DASI announces E-19/9/2002: DASI announces E-mode detection !!mode detection !!

WMAP ResultsWMAP Results

• Temp-Polzn Cross-Power spectra: (l+1)ClTE/2

High low-l modes.

Adiabatic acausal perturbations.

Line based on T-dataonly.(no free parameters.)

CMB Polzn exists! What CMB Polzn exists! What now?now?

• Detection only so far, need to first map Detection only so far, need to first map out the E-mode spectrum into the peak out the E-mode spectrum into the peak region& damping tail & properly region& damping tail & properly measure reionization peak.measure reionization peak.

• Measure B-mode contamination from Measure B-mode contamination from lensing => mass clumping history from lensing => mass clumping history from LSS to now => dark energy?LSS to now => dark energy?

• Eventually measure primordial B-Eventually measure primordial B-modes=> constrain inflation modes=> constrain inflation

How to measure How to measure polarization ?polarization ?

• Measuring such tiny signals inevitably Measuring such tiny signals inevitably involves differencing to minimize involves differencing to minimize systematics and multiple levels of systematics and multiple levels of modulationmodulation

• Broad bandwidths also generally required Broad bandwidths also generally required for sensitivity => Bolometersfor sensitivity => Bolometers

• Need careful foreground identification and Need careful foreground identification and subtraction => multi-frequencysubtraction => multi-frequency

Planck SurveyorPlanck Surveyor

• Planck-HFI Planck-HFI will conduct will conduct all-sky survey all-sky survey to 5’ in 2007-to 5’ in 2007-20092009

Why do it from the Why do it from the ground ?ground ?

• Can in principle obtain much smaller angular Can in principle obtain much smaller angular scales than from satellitescales than from satellite

• Can concentrate on smaller pieces of sky than Can concentrate on smaller pieces of sky than MAP or Planck and go deeper quickerMAP or Planck and go deeper quicker

• Can concentrate on range of multi-poles that Can concentrate on range of multi-poles that offer largest predicted amplitude and best offer largest predicted amplitude and best parameter discriminationparameter discrimination

• Differencing means both polzns go through Differencing means both polzns go through same column of atmosphere - not so sensitive same column of atmosphere - not so sensitive to atm noise as to atm noise as T ground-based experimentsT ground-based experiments

• Can upgrade and repair instrument, more Can upgrade and repair instrument, more flexibility and (a lot!) less costflexibility and (a lot!) less cost

THE QUEST Project THE QUEST Project

• There is a need for a deep (~There is a need for a deep (~K), small area K), small area (10s to 100s sq. deg) polzn experiment which (10s to 100s sq. deg) polzn experiment which will report on a short timescalewill report on a short timescale.

• The Q and U E xtragalactic S ubmm T elescope The Q and U E xtragalactic S ubmm T elescope project aims to fill this gap.project aims to fill this gap.

• It is a joint UK/US project capitalising on It is a joint UK/US project capitalising on expertise and heritage of SCUBA, SuZie, expertise and heritage of SCUBA, SuZie, BOOMERANG and Herschel/Planck, amongst BOOMERANG and Herschel/Planck, amongst many.many.

QUEST Collaboration:QUEST Collaboration:

Cardiff: Cardiff: W. Gear, P.Ade, L. Piccirillo- telescope, W. Gear, P.Ade, L. Piccirillo- telescope, cryogenics, filterscryogenics, filters

Stanford: Stanford: Sarah Church - Focal plane & electronicsSarah Church - Focal plane & electronics

JPL/Caltech: JPL/Caltech: Jamie Bock & Andrew Lange - detectorsJamie Bock & Andrew Lange - detectors

+ K. Ganga (JPL), A. Taylor (Edin)+ K. Ganga (JPL), A. Taylor (Edin)

+ associates+ associates

QQ and and UU EExtragalactic xtragalactic SSubmm ubmm TTelescopeelescope

Flexibility of QUESTFlexibility of QUEST

• A real experiment has a sensitivity of:

skyll

l

fC

T

lC

C 11

)12(

22

pix2/1

(Knox 1995)T – sensitivity/pixel/Stokes parameterpix – pixel size

• Optimum 12pix lCT

Normally in a ground-based CMB Normally in a ground-based CMB experiment one has to chop to remove experiment one has to chop to remove atmosphere. However there is always a atmosphere. However there is always a residual uncancelled emission which often residual uncancelled emission which often dominates the noisedominates the noise

For a polarization experiment however we For a polarization experiment however we difference two polarizations which travel difference two polarizations which travel through the through the samesame column of atmosphere - column of atmosphere - no need to chop - and also makes dish no need to chop - and also makes dish simpler and cheapersimpler and cheaper

Choice of Filter BandsChoice of Filter Bands

• Motivated by Motivated by science – avoid and science – avoid and remove foregroundsremove foregrounds

• Only two Only two frequencies frequencies simplifies the simplifies the design of the design of the refracting refracting reimaging opticsreimaging optics

25.0

25.0

Bandwidth

(%)

165128147Band 2

1058193Band 1

Upper edge

(GHz)

Lower edge

(GHz)

Center

(GHz)

Predicted sensitivitiesPredicted sensitivities0.983347

0.5

0.9

mmp5j

mm1j

mm2j

mm3j

30050 GHzj

50 100 150 200 250 3000.5

0.6

0.7

0.8

0.9

1

0.5 mm PWV1.0 mm 2.0 mm3.0 mm

Frequency (GHz)

Tran

smis

sionFor 1mm PWVFor 1mm PWV

NETs :-NETs :-

100 GHz~0.3100 GHz~0.3

150 150 GHz~0.4mKGHz~0.4mK

The QUEST Focal Plane Design

Each channel will use a Each channel will use a PSBPSB

419143

612100

Beam size Beam size (arcmin)(arcmin)

Number Number of Feedsof Feeds

Frequency(GHz)

QUEST OPTICAL DESIGNQUEST OPTICAL DESIGN

• Wide-field (1.5 degrees), good Wide-field (1.5 degrees), good optical quality (strehl >0.9), optical quality (strehl >0.9), broadband (90-220 GHz)broadband (90-220 GHz)

• On-axis and symmetricOn-axis and symmetric• Cold pupil-stop, small in order Cold pupil-stop, small in order

to fit waveplateto fit waveplate

QUEST OPTICAL DESIGNQUEST OPTICAL DESIGN

Cold Optics OverviewCold Optics Overview

• The lenses and The lenses and waveplate are waveplate are cooled to 4Kcooled to 4K

• All components have All components have a broad-band anti-a broad-band anti-reflection coatingreflection coating

• sapphire waveplate sapphire waveplate is located close to is located close to the cold stopthe cold stop

• The cold stop is The cold stop is located at an image located at an image of the primary mirrorof the primary mirror

Lens 1

Lens 2

Sapphire achromatic waveplate

QUEST TELESCOPE

• QUEST telescope is 2.6m Cassegrain QUEST telescope is 2.6m Cassegrain with foam-cone supporting secondarywith foam-cone supporting secondary

• Designed to rotate around 3 axes - Az, Designed to rotate around 3 axes - Az, El and also centreline of primary (‘Z’)El and also centreline of primary (‘Z’)

• Will point and track +/- 45 deg from Will point and track +/- 45 deg from Zenith with 0.3 arcmin rmsZenith with 0.3 arcmin rms

• Because of novel optical design, Because of novel optical design, cryostat is mounted through centre of cryostat is mounted through centre of primaryprimary

QUEST Site and QUEST Site and scheduleschedule

• Officially begin operations in Chile spring 2004Officially begin operations in Chile spring 2004

• But …….But …….

QUEST on DASIQUEST on DASI

• We have been approached by and are in We have been approached by and are in detailed discussion with the DASI teamdetailed discussion with the DASI team

• Which is likely to result to a late switch to the Which is likely to result to a late switch to the South Pole….South Pole….

QUEST Science GoalsQUEST Science Goals To map CMB polarization on angular scales > 3 Optimized to map E-modes, and B-modes produced by

gravitational lensing and gravity waves

Hu et al. 2002

Planned l-space coverage of QUEST

the largest scales will be determined by scan strategy and the exact science goals

Survey StrategySurvey Strategy

• Two major surveys for separate goalsTwo major surveys for separate goals

• ~1000 sq. deg survey for detailed E-mode ~1000 sq. deg survey for detailed E-mode measurement (~6 months)measurement (~6 months)

• ~30 sq.deg survey for detailed B-mode ~30 sq.deg survey for detailed B-mode measurement (~18 months) to detect measurement (~18 months) to detect lensing signal and possibly primordial lensing signal and possibly primordial gravity waves…..gravity waves…..

E-ModesE-Modes• Maximum (S/N)Maximum (S/N)EEEE ~100. ~100.• 1000 sq degs, 2000hrs1000 sq degs, 2000hrs.

EE

BB, GL

BB, GW

TE-CorrelationTE-Correlation• 1000 sq degs1000 sq degs• Cross-correlate QUEST & WMAP.Cross-correlate QUEST & WMAP.

TT

B-ModesB-Modes• Maximum (S/N)Maximum (S/N)BB BB > 5, detection of B-modes. > 5, detection of B-modes.• 2 x 30 sq degs, 2000hrs.2 x 30 sq degs, 2000hrs.

EE

BB, GL

BB, GW

Comparing QUEST with other experimentsComparing QUEST with other experiments

EE

BB, GW

Cosmological Parameter Cosmological Parameter ForecastsForecasts

mhMatter density

bh Baryon density

h Hubble parameter

Reionisation optical depth

ns Scalar spectral index

Scalar amplitude (~ 8)

r Ratio of scalar to tensors

• Fisher Information Matrix Fisher Information Matrix analysis of cosmological analysis of cosmological parameters.parameters.

• Use a 7 parameter set:Use a 7 parameter set:


bhhnsr

mh

bh

h

ns

2 yr QUEST + 4 yr WMAP

4 yr WMAP


• Factor 3 improvement in r.Factor 3 improvement in r.

• Factor 2 improvement in nFactor 2 improvement in nss.

4 yr WMAP

2 yrs QUEST +

4 yrs WMAP

Science SummaryScience Summary

QUEST will measure EE-Power with s/n=100 over very large l-range – reionisation? Neutrinos?

Should detect and measure BB-Power Spectrum. Cosmological Parameters: 2 yr QUEST will

improve 4 yr WMAP by factors 2-3. Main improvement on ns & r, so stronger

constraints on inflation. Test isocurvature modes from Inflation. Test for non-Gaussianity. Direct measure of P(k) from grav lensing. Due to start early 2005 & run for 2 yrs.

Future Plans ….Future Plans ….

• QUEST and other plannned QUEST and other plannned experiments will only measure experiments will only measure T/S~0.05-0.1T/S~0.05-0.1

• To go deeper requires more sensitivity To go deeper requires more sensitivity and systematic rejectionand systematic rejection

• Lensing contamination probably means Lensing contamination probably means a limit >0.001a limit >0.001

• NASA already planning a dedicated B-NASA already planning a dedicated B-mode satellite ~2015 mode satellite ~2015

Future PlansFuture Plans

• These ‘4th generation’ experiments will require These ‘4th generation’ experiments will require ~x100 improvement in sensitivity and systematic ~x100 improvement in sensitivity and systematic rejectionrejection

• We (Cardiff&Cambridge) planning a UK We (Cardiff&Cambridge) planning a UK programme of ground-based and possibly balloon-programme of ground-based and possibly balloon-borne B-mode experimentsborne B-mode experiments

• We believe a combination of the existing We believe a combination of the existing bolometer technology with interferometric bolometer technology with interferometric imaging is the way to achieve this……… but that imaging is the way to achieve this……… but that is another seminar entirely ! is another seminar entirely !

Documents

The “QUEST” for CMB Polarization