systematicswg:telecons:2018-01-31:start [Probe Mission Study Wiki]

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==== 2018-01-31 ====

  * Agenda:
    * Updates on work in progress
    * Polarization Angle Accuracy


=== Polarization Angle ===

Uncertainty in polarization calibration creates EB leakage. Sacrifice cosmic birefringence limits to zero TB,TE,EB. Improvement of calibration sources: difficult across broad bands and large. Onboard calibrator? Compact polarized source measurements should be revisited? Hardware solution potentially?  

  * Analysis:
    * Planck:
      * [[https://www.aanda.org/articles/aa/full_html/2010/12/aa13054-09/aa13054-09.html | Planck HFI ground calibration]] measured detector polarization angles to ~ 1  degree relative uncertainty and claimed 0.3 degrees absolute uncertainty.
      * [[https://www.aanda.org/articles/aa/abs/2016/12/aa28890-16/aa28890-16.html | Planck HFI inflight measurement check]] using TB and EB(in section A.6 of the linked paper) claimed a sensitivity of about 0.2 degrees on the absolute angle, and the pre-flight measurements were not adjusted.  Crab measurements were much more uncertain but 
      * A baseline simulation could thus include 0.3 degree random absolute error and 0.9 degree random relative errors.
      * We probably only need one absolute error, this is probably scalable to 0.2 degrees if we really want to.
    * Eric Hivon's [[https://zzz.physics.umn.edu/ipsig/mcsim_angles | simulations]]
    * Analytical Estimation of cross-pol errors:
      * {{:systematicswg:telecons:2018-01-31:matias_cross-pol_20060709.pdf| Matias Cross Pol Memo for EBEX from 2009}} based on this [[https://arxiv.org/abs/astro-ph/0210096 | paper by Hu, Hedman, Zaldarriaga]]
      *  Brendan reaction: 
        * I think the one about cross pol agrees with what we’ve been saying: 1. we’re don’t need to worry too much about the relative polarization calibration of individual detectors because they can be calibrated very well against the others.  2. checking that <EB> and <TB> are nonzero can give you the overall polarization angle.  No other magic bullets unfortunately.
        * We could use the analytic formulas from this memo to write down what leakage into BB we get if we have an overall polarization angle error at the level of say, Planck.   So we could get an idea of the issues we’d have if we didn’t sacrifice the birefringence science.
      * Re-do analysis with PICO sensitivity estimate?
      * Investigate how much we really lose any birefringence science?


Some more references:
  * [[http://iopscience.iop.org/article/10.1088/2041-8205/762/2/L23/meta | SELF-CALIBRATION OF COSMIC MICROWAVE BACKGROUND POLARIZATION EXPERIMENTS by Keating, Shimon and Yadav]]
  * See more references in the systematics table
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