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The “QUEST” for CMB Polarization

The “QUEST” for CMB Polarization. Walter K. Gear Cardiff University. Talk Structure. CMB Review Why Polarization ? The QUEST Experiment (Future Plans). Curtesy Wayne Hu htp:\background.uchicago.edu. CMB: Cosmic Rosetta Stone.

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The “QUEST” for CMB Polarization

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  1. The “QUEST” for CMB Polarization Walter K. Gear Cardiff University

  2. Talk Structure • CMB Review • Why Polarization ? • The QUEST Experiment • (Future Plans)

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

  4. CMB: Cosmic Rosetta Stone... • CMB arises from last-scattering surface ~300,000 years after the Big Bang • This is the earliest direct image of the Universe we can ever obtain (EM anyway…) • The imprints of structure of the Universe today AND BigBang/inflation should also be imprinted there...

  5. Constraining 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):

  6. Inflation predicts a mixture of scalar (pure density) and Tensor (gravity wave)fluctuations • The precise ratio is a function of the type of field which causes inflation • Scalar fluctuations couple to matter and provide the “seeds” for structure formation • Tensor perturbation causes a ‘background’ of gravity waves Scalars and Tensors

  7. CMB: The Golden age….

  8. Temperature power spectra

  9. CMB: The Golden Age …..

  10. 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

  11. The MAP Temperature results…..

  12. “With temperature data alone, r of less than ~0.1 cannot be detected, no matter how accurate the measurement” (Kinney 1999 astroph/9806259) • With polarization data however we can break this degeneracy (amongst others) The anisotropy measurements have been a triumph, BUT ….

  13. The power of polarization… • Fundamental prediction of standard theory, if not detected at mK then there would be real problem • The extra information provided by polarization allows much better constraints on some vital cosmological parameters - 4 power spectra rather than 1. • Combination of P and DT improves some parameter constraints by factors 2-3 in most models • Break degeneracy between intrinsic fluctuation amplitude and re-ionization • Separate scalar and tensor modes in the initial fluctuation spectra, if B as well as E modes can be detected

  14. It is convenient to write this is as the sum of the gradient and curl of a scalar and vector field E and B [but has nothing to do with E and B EM fields !!] Temperature is a scalar but Polarization is a second-rank Tensor

  15. E and B modes • The scalar function E represents pure density fluctuations • The tensor function B represents metric fluctuations - gravity waves

  16. P = Q + U Polarisation of the CMB Temperature Q U • Generated by Thompson scattering off electrons in quadrupolar motion. + Polarisation Matrix:

  17. E E B B E/B Decomposition Cold Spot Hot Spot • Can decompose Q,U into: • E-modes (even-parity): • B-modes (odd-parity): • E-modes generated by scalar & tensor perturbations. • B-modes generated by tensors & grav. lensing.

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

  19. CMB polarisation spectra • Have 4 possible spectra:TT, TE, EE, BB. • TB = EB = 0by parity. Sachs-Wolfe Silk Damping Acoustic Oscillations Gravitational Lensing Reionisation Gravitational Waves

  20. 19/9/2002: DASI announces E-mode detection !!

  21. WMAP Results • Temp-Polzn Cross-Power spectra: (l+1)ClTE/2p High low-l modes. Adiabatic acausal perturbations. Line based on T-data only. (no free parameters.)

  22. CMB Polzn exists! What now? • Detection only so far, need to first map out the E-mode spectrum into the peak region& damping tail & properly measure reionization peak. • Measure B-mode contamination from lensing => mass clumping history from LSS to now => dark energy? • Eventually measure primordial B-modes=> constrain inflation

  23. How to measure polarization ? • Measuring such tiny signals inevitably involves differencing to minimize systematics and multiple levels of modulation • Broad bandwidths also generally required for sensitivity => Bolometers • Need careful foreground identification and subtraction => multi-frequency

  24. Planck Surveyor • Planck-HFI will conduct all-sky survey to 5’ in 2007-2009

  25. Why do it from the ground ? • Can in principle obtain much smaller angular scales than from satellite • Can concentrate on smaller pieces of sky than MAP or Planck and go deeper quicker • Can concentrate on range of multi-poles that offer largest predicted amplitude and best parameter discrimination • Differencing means both polzns go through same column of atmosphere - not so sensitive to atm noise as DT ground-based experiments • Can upgrade and repair instrument, more flexibility and (a lot!) less cost

  26. THE QUEST Project • There is a need for a deep (~mK), small area (10s to 100s sq. deg) polzn experiment which will report on a short timescale. • The Q and U E xtragalactic S ubmm T elescope project aims to fill this gap. • It is a joint UK/US project capitalising on expertise and heritage of SCUBA, SuZie, BOOMERANG and Herschel/Planck, amongst many.

  27. Q and UExtragalactic Submm Telescope QUEST Collaboration: Cardiff: W. Gear, P.Ade, L. Piccirillo- telescope, cryogenics, filters Stanford: Sarah Church - Focal plane & electronics JPL/Caltech: Jamie Bock & Andrew Lange - detectors + K. Ganga (JPL), A. Taylor (Edin) + associates

  28. Flexibility of QUEST • A real experiment has a sensitivity of: (Knox 1995) • T – sensitivity/pixel/Stokes parameter • pix – pixel size • Optimum

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

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

  31. Center (GHz) Lower edge (GHz) Upper edge (GHz) Bandwidth (%) Band 1 93 81 105 25.0 Band 2 147 128 165 25.0 Choice of Filter Bands • Motivated by science – avoid and remove foregrounds • Only two frequencies simplifies the design of the refracting reimaging optics

  32. Predicted sensitivities For 1mm PWV NETs :- 100 GHz~0.3 150 GHz~0.4mK

  33. Frequency (GHz) Number of Feeds Beam size (arcmin) 100 12 6 143 19 4 The QUEST Focal Plane Design • Each channel will use a PSB

  34. QUEST OPTICAL DESIGN • Wide-field (1.5 degrees), good optical quality (strehl >0.9), broadband (90-220 GHz) • On-axis and symmetric • Cold pupil-stop, small in order to fit waveplate

  35. QUEST OPTICAL DESIGN

  36. Lens 1 Lens 2 Sapphire achromatic waveplate Cold Optics Overview • The lenses and waveplate are cooled to 4K • All components have a broad-band anti-reflection coating • sapphire waveplate is located close to the cold stop • The cold stop is located at an image of the primary mirror

  37. QUEST TELESCOPE • QUEST telescope is 2.6m Cassegrain with foam-cone supporting secondary • Designed to rotate around 3 axes - Az, El and also centreline of primary (‘Z’) • Will point and track +/- 45 deg from Zenith with 0.3 arcmin rms • Because of novel optical design, cryostat is mounted through centre of primary

  38. QUEST Site and schedule • Officially begin operations in Chile spring 2004 • But …….

  39. QUEST on DASI • We have been approached by and are in detailed discussion with the DASI team • Which is likely to result to a late switch to the South Pole….

  40. QUEST 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 the largest scales will be determined by scan strategy and the exact science goals Planned l-space coverage of QUEST Hu et al. 2002

  41. Survey Strategy • Two major surveys for separate goals • ~1000 sq. deg survey for detailed E-mode measurement (~6 months) • ~30 sq.deg survey for detailed B-mode measurement (~18 months) to detect lensing signal and possibly primordial gravity waves…..

  42. EE BB, GL BB, GW E-Modes • Maximum (S/N)EE ~100. • 1000 sq degs, 2000hrs.

  43. TE-Correlation • 1000 sq degs • Cross-correlate QUEST & WMAP. TT

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

  45. Comparing QUEST with other experiments EE BB, GW

  46. Cosmological Parameter Forecasts • Fisher Information Matrix analysis of cosmological parameters. • Use a 7 parameter set: Wmh2 - Matter density Wbh2 - Baryon density h -Hubble parameter t - Reionisation optical depth ns-Scalar spectral index A - Scalar amplitude (~ s8) r - Ratio of scalar to tensors

  47. Cosmological Parameter Forecasts DWmh2 DWbh2 Dh Dt Dns DA DWbh2 Dh Dt Dns DA Dr 4 yr WMAP 2 yr QUEST + 4 yr WMAP

  48. Cosmological Parameter Forecasts • Factor 3 improvement in r. • Factor 2 improvement in ns. 4 yr WMAP 2 yrs QUEST + 4 yrs WMAP

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