CMB B-mode Polarization Experiments:
First Results from POLARBEAR (and BICEP2)Haruki Nishino (Kavli IPMU)@ICRR/IPMU ACP seminar 2014-06-05

“Major discovery!” by BICEP2

You might already know well the BICEP2 result…
Any progress so far after then?

2Just a week before the BICEP2 paper…

•

POLARBEAR published the best B-mode measurement at subdegree scale!

3

First result from ACTpol is out too.

•

Only three months of data.

•

High-ell E-mode power spectrum measurement•

B-mode power spectrum is null consistent.

4

First Results from POLARBEAR• “A Measurement of the Cosmic Microwave Background B-

Mode Polarization Power Spectrum at Sub-Degree Scales with
POLARBEAR” (http://arxiv.org/abs/1403.2369)• Best measurement of B-mode auto-power spectrum in sub-degree angular scale• “Gravitational Lensing of Cosmic Microwave Background

Polarization” (http://arxiv.org/abs/1312.6646, accepted at PRL)
• First evidence for gravitational lensing with CMB

polarization data alone• “Evidence for Gravitational Lensing of the Cosmic Microwave

Background Polarization from Cross-correlation with theCosmic Infrared Background” (PRL 112, 131302 (2014))• Cross-correlation with CIB, confirmation of SPTpol result

Measurement of lensing B-modes with three independent methods

5Cosmology with CMB B-modes
Primordial Gravitational Wave from Inflation• GUT-scale ultra high energy physics• Weak Gravitational Lensing from Large Scale Structure• Sum of neutrino mass•

Cosmic Microwave Background
CMB Temperature Power Spectrumby Planck

2.7K with 10-5 fluctuation

CMB can be described by 2-point
correlation function (power spectrum)
because of the Gaussianity.

1
*
Cl =
alm alm∑
2l +1 mPhysics in the early universe is imprinted in CMB.

Thomson scattering makes
linear polarization

Wayne Hu (http://background.uchicago.edu/~whu/intermediate/Polarization/polar1.html)

8Local quadrupole anisotropy+Thomson scattering
induced CMB polarization
Hot

Cold

Cold
Hot
Wayne Hu (http://background.uchicago.edu/~whu/intermediate/Polarization/polar1.html)

9Density-wave (scalar perturbation)
A density wave produces temperature anisotropy.
wave vector k

Hot

Cold

Hot

Cold

Hot

Cold

Hot

Cold

Locally, electrons
see quadrupole
anisotropy.
10Density-wave (scalar perturbation)
Polarization pattern produced by the density wave
wave vector k

Hot

Cold

Hot

E-mode: Polarization orientation
is parallel or perpendicular to
the wave vector, k.
No polarization change by thesign ﬂip of k.

Cold

Hot

Cold

Hot

Cold

line of sightobserver11

E-mode and B-mode

•

E<0

B<0

E-mode (grad):even parity

B-mode (curl):
odd parity

Polarization fields can be decomposed into two
orthogonal fields of E- and B-modes•

Density perturbations (which have been seen as
temperature fluctuation) can only create E-mode.
12

Inflation(Fig. from BICEP2 team)60-35

Accelerating expansion (~e ) in 10 seconds• Two types of perturbations were generated during inflation fromquantum fluctuations• Scalar (density) perturbations• Tensor perturbations = Gravitational wave•

13

Gravitational wave (tensor perturbations)
Gravitational wave
(two orthogonal modes)“+” modesqueezed

wave vector k

stretchedsqueezed
stretched

stretchedsqueezed

stretchedsqueezed“x” modesqueezed

stretchedsqueezed

stretched

stretched stretchedstretched
stretchedsqueezedsqueezedsqueezedsqueezed

stretchedsqueeze

stretchedsqueezed
stretched

stretchesqueezed

stretchedsqueezedsqueezed squeezed
stretched
14

Local quadrupole from gravitational wave
Gravitational wave produces local
quadrupole temperature anisotropies

Cold

Cold

Cold

“x” mode
Cold

Cold

Hot

Cold

Hot

Cold

Hot

Cold

Hot

Cold

Hot

Hot
Cold

Hot

Cold

Hot

Hot

Hot

Hot

Cold

Hot

Cold

Hot

“+” mode

wave vector k

Cold

Hot

Cold

Hot

Hot

Cold

15

Polarization pattern by gravitational wave
Polarization pattern generated
by the quadrupole

Cold

Cold

Cold

“x” mode
Cold

Cold

Hot

Cold

Hot

Cold

Hot

Cold

Hot

Cold

Hot

Hot
Cold

Hot

Cold

Hot

Hot

Hot

Hot

Cold

Hot

Cold

Hot

“+” mode

wave vector k

Cold

Hot

Cold

Hot

Hot

Cold

16

Polarization pattern by gravitational waveLetʼs consider the polarization projection on
to the last scattering surface like this.

Cold

Cold

Cold

“x” mode
Cold

Cold

Hot

Cold

Hot

Cold

Hot

Cold

line of sight= normal to the display

Hot

Cold

Hot

Hot
Cold

Hot

Cold

Hot

Hot

Hot

Hot

Cold

Hot

Cold

Hot

“+” mode

wave vector k

Cold

Hot

Cold

Hot

Hot

Cold

last scattering surface
observer17Polarization pattern by gravitational waveLetʼs consider the polarization projection on
to the last scattering surface like this.

wave vector k (projected)“+” mode“x” mode

last scattering surface18E-mode from gravitational wave
wave vector k (projected)“+” mode
E-mode“x” mode19

B-mode from gravitational wave
wave vector k (projected)

Polarization orientations can bechanged by the sign ﬂip of k.

B-modeB-mode: Polarization
orientation is 45 or 135
rotated to the wave vector, k.

“x” mode20

Scalar/Tensor Perturbations•

Scalar perturbations:••

CMB power spectra
ScalarProduces CMB
Temperaturefluctuation (and Emode polarization)

Tensor(Grav. Wave)

Tensor perturbations:
Gravitational Wave•

Tiny effect in T or E•

But produces B-mode
polarization too•

Unique prediction
from inflation!

arXiv:1210.6008

scaled by “r” (tensor-to-scalar ratio)21

Quantitative Study of Inflation w/ B-mode•

Energy scale of inflation directly relates to the ratio of tensor
and scalar perturbations
n −1
n
•

Tensor-to-scalar ratio:
•

•
•

At
r≡
As

"k%s
P s= As$ '# k0 &"k%t
P t = At $ '# k0 &

Proportional to B-mode power spectrum

Inflation potential:€V1/4 ~ (r/0.01)1/4 x 1016 GeV€€

Detecting B-mode in large angular scales proves inflationand enables quantitative study of models of inflation.
•

Also a probe of physics of ultra high energy scale (~GUT
scale)•

r=0.2 → energy scale of inflation: 2 x 1016 GeV
22

Another B-mode source:
Gravitational Weak Lensing(image credit: ESA)CMB

z~1100now
Observed CMB has been deflected by gravitational potentials of
Large Scale Structure from z~1100 up to now.
23

CMB Polarization and Weak Lensing
10x10degPrimordial
CMB
E-modeWeak
Lensing“Lensed”
CMB
E-mode“Lensed”
CMB
B-modeFig. from astro-ph/0111606

Gravitational lensing mixes E-mode and B-mode.
• Primary B-mode source in small angular scale (subdegree).
•24

CMB Polarization and Weak Lensing
Observed CMB polarization(Q + iU )(nˆ ) = (Q˜ + iU˜ )(nˆ + d(nˆ ))deflection angle!
~: primordial CMB(weak lensing effect)•

Typical deflection angle: a few arcmin•

Coherent over ~2 deg. scale

Requires degree-scale observation with atelescope of arc minute resolution
25

Weak Lensing and Neutrino Mass•

Massive neutrinos suppress the evolution of large
scale structures.

Lensing potential power spectrum

Higher neutrino mass↓
Less large-scale structure↓
Smaller lensing effectPlanck 2013 (lensing)w/ WMAP pol.+SPT+ACT
Σ(mν) < 0.85 eV (95%CL)
arXiv:1303.5077
26

Upper limits of B-mode power
spectrum before March 2014
From BICEP1-3yr paper

arXiv:1310.1422

Lensing B-mode
Primordial B-mode
BICEP

Large angular scale•(r=0.1)First season
POLARBEAR

Small angular scale

SPTpol claimed the “detection of B-mode“ by the cross-correlation withgalaxy, but BB auto-correlation spectrum from SPTpol is not published yet.

27

CMB polarization
experiments

CMB polarization experiments•

Satellite: PLANCK•

Balloon-borne: EBEX, SPIDER•

South Pole•

Need thin and dry atmosphere

BICEP and Keck Array

SPT
BICEP

•
•

SPTpolKeck

Atacama Desert, Chile•

POLARBEAR•

ACTpol•Atacama B-mode Search (ABS)

POLARBEAR

ABS

ACT

29

POLARBEAR••

Ground-based CMB
polarization experiment in
the Atacama desert•

5,200m altitude•Thin and dry atmosphereStarted observation since
early 201230

POLARBEAR Collaboration
PI: Adrian T. Lee!
(UC Berkeley)

International collaboration from 5countries, ~70 researchers
31

POLARBEAR site

Northern Chile

32

POLARBEAR site
Atacama Desert

33

Atacama desert
POLARBEAR,
ACT, ABS~5200mTAO~5640m(world highest)

ASTE, NANTEN~4860mALMA(QUIET)~5000m34

Huan Tran Telescope
CMB photon

Primary mirror•

Off-axis Gregoriane Dragone•

3.5m Primary mirror

3.5m

Secondary mirror•

3.5 arcmin (FWHM) resolution•

designed to measure bothprimordial and lensing Bmodes

Receiver cryostat
35

POLARBEAR Receiver

Focal Plane (cooled to 0.25K)

HWP (polarization modulation)
36

Focal Plane Detector Arraydual-polarization
dipole slot antenna

1mm

2 bolometers in a pixel• 637 pixels in a array• 1274 bolometers (~80% yield)•

Noise level: 550 uKs1/2 /bolo
23 uKs1/2 /arraymicrostrip
bandpass
filter (150GHz)

Al/Ti bi-layer
TES bolometerphoton
↓
Temp↑
↓
R↑
↓
current↓(V-biased)
37

Polarization measurement bypair-diﬀerencing
B!
A!

Pair bolometers in a single pixel aresensitive to linear polarizations, which
are perpendicular to each other.

Pixel differencing gives us a polarization information ofincident light.
It is also effective for common mode noise rejection.

Good beam (and gain) matching between pairdetectors is crucial because the mismatch canpotentially cause leakage from T->P.
38

BICEP/Keck Array
BICEP

•

Keck Array

CMB polarization experiments at South Pole•

Target large angular scales, i.e. the primordial
gravitational wave B-modes
39

Spec. Summary of BICEP/KeckOperation Time
Frequency
Detectors
Noise level
(uK s
Beam
(Resolution)

BICEP1BICEP2

Keck Array≒

2006-20082010-2012

2011-

2014

100/150 GHz

150 GHz150GHz(100GHz)100GHz98
NTD GeDetectors
54 (/array)

512 TESbolometers2560 TES
bolometers2560 TES
bolometers

16 (/array)~10 (/array)

0.52° FWHM

0.52° FWHM

0.93°/0.60°
FWHM

comparable to SPTpol,
POLARBEAR, etc

BICEP30.37° FWHM

optimized forlarge angular scale

BICEP/Keck also empolys similar detector technique(TES bolometers + pair-differencing).
40

Observed Sky Region
Planck 857GHz map•

Choose low astrophysical “foreground” regions

POLARBEAR: 3 small sky regions (3°x3°): ~30 deg2
• BICEP: ~380 deg2, fsky~2%•41

Telescope scan•

Always scanning in azimuth (horizontally) at each constant elevation•

To see the modes before detector gain drifting.

42

CMB Data Analysis•

Calibration: Gain, Pointing, Beam, Polarization angle…

•

Data Selection: Bad weather, Badly tuned detectors…

•

Map-making: I, Q, U maps of each field (for each day)•Power spectrum: Cross-spectrum with each-day-maps•

Null Tests (Jackknife): data validation, systematics check•

Systematic Error: Estimate leakage from T, E → B
43Beam Measurement
POLARBEAR

BICEP2(coadded map of Saturn)Circular beam with 3.5’ FWHM

0.52° FWHM
44

CMB Polarization Maps (POLARBEAR)
Q=EX2-EY2

X

Y
U=EA2-EB2

B

A(Filtered) map noise level: 5 uK-arcmin• ~10 times deeper than Planck• Deepest map in this scale ~ BICEP2•45

BICEP2 CMB Maps

RMS noise level of 87 nK in 1° x 1° pixel

46

BICEP2 E-mode & B-mode maps

Impressive demonstration of E and B modes.
We can see B-modes in map space.

47

Null Tests (Jackknife)
CMB Data

Data inbetterweather

Data inworse
weather

Cl in better
weather

Cl in worse
weather-

Split the data into two with somecriteria to illuminate some possible
systematic effect
Subtract spectra with each otherand Check if the residual spectrum isnull or not.

= Null?

If there is a systematic bias between the two data set,
the difference spectrum would not be null.
• BICEP2 did this in a map space.
•48

Null Tests (POLARBEAR)•First half vs. Second half•

Rising vs. Setting•High vs. Low elevation•

High vs. Low gain•

Good vs. Bad weather•

Pixel polarization angle orientation type•Left vs Right side detectors•

Left vs. right-going scan•Moon distance49

Null Test PTEs
POLARBEAR

BICEP2 PTE (each spectrum)

PTE (each bin)PTE (each spectrum)!
PTE (each null test)

using only first 5 bins

No significant systematics found50

(After passing all the null tests…)
B-mode power spectra(BB power spectrum was blinded for POLARBEAR.)

Comparison with other upper limits (3/10)

95% CLupper limit

AL = 1.12 ± 0.61 (stat.)+0.04-0.10 (sys.) (AL = 1: WMAP-9yr ΛCDM)
Rejection of null hypothesis (AL>0) at 97.5% CL

52Comparison with other upper limits (3/17)

53

BICEP2 BB spectrum
Very low PTE with the solid line
(lensed ΛCDM)• 5.3σ detection of the excess
power at low-ell• What about the excess aroundell~200?
• “We caution against overinterpretation of the two highband powers at ell~220 — theirjoint significance is less than 3σ”•

These might be just statistical fluctuations, ormight be an indication for unknown systematics?
54

Cross-spectrum w/ Keck Array
If there are any
systematics only in
BICEP2 data,
the cross correlation of
BICEP2xKeck should
show significantly
different result.

•

The cross-spectrum with Keck Array shows better fit with lensed ΛCDM+r>0
although it looks significantly different from the BICEP2 auto-spectrum.
• This adds some confidence for non-zero r detection.
• But this might also indicate unknown systematic contamination of
BICEP2.
55

Constraint on r from BICEP2
Error bars include
sample variance.

•

r=0.20+0.07-0.05, 7.0σ r>0 detection• w/ foreground subtraction (DDM2): r=0.16+0.06-0.05, 5.9σ
detection• (Best-fit r ranges between 0.12 ~ 0.21 depending on themodel or the treatment of foreground)
56

Then, what is going on now?

57

Some worrying systematics•

Instrumental systematics•

Foreground contamination

58

Most worrying (instrumental) systematics for BICEP2:
Diﬀerential Beam Systematics•

Pointing mismatch: Differential pointing can cause aserious leakage from temperature fluctuation to Bmode polarization.

Other differential beam effects

beam size

pointing

ellipticity

gain

59

Diﬀerential beamsystematics and“deprojection”

diﬀ. pointing
deprojection
relative gain•

Differential beam effect canbe mitigated by“deprojection” technique inthe BICEP2 data analysis
using Planck T map.

•

Without the deprojection,observed ClBB would bedominated by the leakage
from ClTT by differential
pointing and relative gain
mismatch.

deprojection

Waiting for details in the coming systematics paper…
60

Systematic
uncertainty (BICEP2)• Every systematic

uncertainty is estimatedto be negligible.

Waiting for details in the coming systematics paper…
61

Systematic uncertainty (POLARBEAR)
Expected B-mode

Estimated foreground ismuch smaller comparedwith either stat or sys error.

combined error
pointing
differential beam size
polarization angle
differential ellipticity
relative gain (HWP dependent)
relative gain
electrical crosstalkgain drift

Negligible leakage without deprojection
62

Astrophysical foregrounds (BICEP2)

Dashed lines: autospectra of models• Solid lines: crossspectra with BICEP2
maps
•

•

DDM: “Data Driven Model” constructed from publicly available Planck data
products. The Planck dust model map at 353GHz is scaled to 150 GHz.

What is wrong with this?

63

It seems BICEP2 used the Planck map image
presented at a conference by digitizing it.
They estimated the polarization fraction to be 5%.
However, this map is not CIB (cosmic infrared
background) subtracted, which could result inunderestimating pol. fraction.

64

Recent Planck dust polarization fraction map

Polarization fraction in low intensity region: ~8%60% higher than BICEP2’s assumption
Effect on power spectrum should be 1.62

arXiv:1405.7351

arXiv:1405.0871

Recent Planck showed higher polarization
No one knows fraction
the answer…
Wait for dust.
Planck’s next release.
of galactic

65

Other analysis results from
POLARBEAR

Optimal Estimator for Gravitational Lensing•

Gravitational lensing induces correlation between
different multipoles (l and l’) of E-mode and B-mode.
• We can make use of the correlation to estimate thelensing deflection field, d(L).

dEE (L) ∝ ∑ E(l)E(l#)
ldEB (L) ∝ ∑ E(l)B(l#)
larXiv:1312.6646

CLdd = <dxdx’*>€“4-point correlation” with only
CMB polarization data alone

l’

l
L

(Hu, Okamoto, 2002)

PRL 113, 131302 (2014)

CLdI = <dx, CIB>
Cross-correlation with CIB (biased
tracer of dark matter halos)
67Combined lensing power spectra<EEEB>!
<EBEB>!
Combined
AL=1.37+/-0.30 (stat.)+/-0.13 (sys.)(AL=1: ΛCDM w/ WMAP9)

AL: Lensing amplitude

Consistent between <EEEB> and <EBEB>.
• 4.2 σ rejection of null hypothesis• First detection (evidence) for gravitational lensing with CMB
polarization alone•68

Cross-correlation with CIB
dEB !
x CIB
dEE
CIB: Herschel/SPIRE~500um!
!

CIB is a good tracer
for the matter
distribution in z=1~3.!
→ Should correlatewith CMB lensing.
Reject null hypothesis at 4.0 σ• Consitent with SPTpol (Hanson et al, 2013)•

69

POLARBEAR-2 & Simons Array
New POLARBEAR-2
receiver developed by KEK

Multichroic antenna(90+150GHz)+TES bolometer

Two new telescopes (Simons Array)+

POLARBEAR-2 will be deployed in 2015
• Confirm and measure r. Characterize B-mode better• Constrain sum of neutrino mass: σ ~ 20 meV (w/o sys.)•70Summary•

BICEP2 detected B-mode power at degree angular scale•

Detection of non-zero r at > 5 σ, r=0.1~0.2•

Recent discussions on foreground suggest that thedetection of the cosmological signal is not conclusive.
••

Needs confirmations from other experiments!

POLARBEAR measured B-mode power spectrum with thebest sensitivity at sub-degree angular scale.
•

Detected gravitational lensing with three independent
methods (at > 4σ)•

POLARBEAR is starting large angular scale observations.

“New era of B-mode cosmology has begun.”71