Thoughts on Ground-based lensing measurements Chao-Lin Kuo Stanford/SLAC KIPAC

The primordial, Gaussian E-polarization

Large Scale Structure

B-polarization J Tolan

Lensing B-polarization is a LSS experiment Deep polarization measurements (4  K rms) on 1.5% of the sky can significantly improve Planck+SNAP constraints on {w 0, w a,  k, ∑m }, p  =w   w=w 0 +w a (1-a) There is a strong theoretical preference: w 0 = -1, w a =0,  k <10 -4 → lensing B provides a constraint on ∑m Hu, Huterer and Smith, 2006

The Status of B-Polarization Measurements (07/2009) QUaD/BICEP (50~100 detectors) still miss the (lensing) B-polarization by ~ 2 orders of magnitude. The current round of experiments (~1000 detectors) can only hope for a statistical detection. To perform high S/N imaging of lensing B-polarization, one must increase the survey speed by The ground based platforms (DASI “drum”, SPT) will be maxed out already in the current round of exp. Chiang et al. Lensing B-mode Gravity wave r=0.1

The simple strategy to get ~10,000 detectors on the sky… Use an optical design that has the largest possible focal plane area Choose an aperture size that optimizes throughput/dollar

Optics Comparison H. Tran et al., CMBPOL Technology Workshop, 2008 Crossed Dragone Gregorian Strehl Ratio The advantage of a crossed-Dragone system (1). > 4X more FOV area than a Gregorian (2). Flat/telecentric focal plane, no re-imaging Optics -Good polarization properties verified in numerous studies The required primary aperture for lensing B-mode is ~2 meters – for 10m class telescopes the measurements will be sensitivity (throughput) limited, not resolution limited.

The simple strategy to get ~10,000 detectors on the sky… Use an optical design that has the largest possible focal plane area Choose an aperture size that optimizes throughput/dollar The Proposed Experiment:The Proposed Experiment: An array of 5-10 crossed-Dragone multifrequency telescopes, each with ~2-meter primary aperture and ~2,000+ detectors An array of 5-10 crossed-Dragone multifrequency telescopes, each with ~2-meter primary aperture and ~2,000+ detectors

A Pilot Project: one 1.5-2m telescope Serving as the prototype for two experiments –Pol-Len: Polarimeter array for Lensing –EPIC-IM (in collaboration w/ JPL) The telescope will be integrated with –Room temperature sources/detectors –A BICEP-2 style 512-detector bolometric receiver –A larger format camera – see the next page Many issues can be characterized in full details with this pilot projet: –Near and far sidelobe responses, baffling –Infrared filtering –Magnetic field shielding –Detector loading –Mitigation of polarization systematics

The expansion prospects 1 Telescope * bolometers 1 Telescope + 2,000 bolometers 5 Telescopes, each w/ 2,000 bolometers LDRD funds 1 Telescope Deployment for field observations (minor technology dev. required) 1 Telescope + 8,000 bolometers 5-10 Telcps., each w/8,000 detectors (major technology dev. required) EPIC-IM mission * # of detectors projected for 150 GHz data/design feedback

warm baffle receiver cryostat Vacuum window The “major” technology development By reducing the size of the feeds we can pack more detectors (~4x) onto the focal plane (~1.5 f ) The price to pay is increased spillover – which must be intercepted at 4K 8,000 detectors to read per dewar Zotefoam Teflon (50 k) HR-10 OFHC (4K) IR filter cold stop

Also a great gravity wave B-mode experiment (for r<0.1) Smaller maps → lower noiseSmaller maps → lower noise Smaller maps → potentially less foregroundSmaller maps → potentially less foreground Small beams → de-lensing possibleSmall beams → de-lensing possible Small beams → less Beam systematicsSmall beams → less Beam systematics Compared to degree beam experiments (BICEP/Keck, ABS), a 2 m class telescope offers: 3.6 deg 7.2 deg 14.4 deg 28.8 deg (Polarized Dust, 5%)

The Trade-offs No Half-Wave-Plate modulators. No full - rotation. Modulation relies on scanning – QUaD/BICEP style. For the same, 2 possible angles can serve as a systematic check.

Funding/fielding prospects SLAC “LDRD” under review (1 telescope, warm tests) An NSF proposal will go in this August (“Pol-Len1”, one telescope +mount+ receiver development) BICEP/Keck collaboration supportive of the deployment of the telescope to the South Pole DSL site in Pending approval from NSF-OPP (office of polar programs). We have not thought about how to fund the full array…Let me know if you have $ or are interested.

The End. Question?