Future Experiments

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Experiment Energy (GeV) dA/A Compton

Edge (MeV)C-edge/0xing displacement

HAPPEX-II 3 1.2% 158 12mm/6.5mm

PREX-II 1 1% 35 6mm/3mm

CREX 2.2 3.3% 160 12mm/6.5mm

MOLLER 11 2% 3100 48mm / 28mm

SOLID PVDIS 11, 6.6 0.5% 1260 (32mm/

18mm)

Status Summary • PREX-I demonstrated 1% at 1 GeV from integrating photon analysis. Dominant

error: laser polarization measurement - should be improved PREX-II• CREX should be easier than PREX in photon detector, and e-det analysis will be

possible to improve precision• MOLLER/SOLID - collaboration working group evaluating critical upgrade plans to

meet very challenging ultimate goal of <0.5% accuracy

Upgrade

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e- det: • Not necessary (but perhaps useful?) for PREX• Useful (though perhaps not truely necessary?) for CREX• Must be optimized for high precision for MOLLER/SoLID• uniform efficiency is highly important to assist calibration

γ det: • existing detector ideal for PREX and CREX• upgrade needed for high energy (MOLLER/SoLID)

Synch light field extensions:• Needed for 11 GeV - already planned for installation• Field mapping already planned

Counting DAQ:• No counting analysis at high flip rate without it. • Needed for PREX (only if using e-det), CREX (only for reliability)• Necessary for 11 GeV

Laser Polarimetry:• New (qweak) techniques require improved initial state control • New diagnostics should also be useful

Beam aperture:• Backgrounds are higher than residual gas - improved operability

should be expected at low E and especially high energy

Upgrade Components

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Experiment Synch Shield e- det counting

DAQnew

photon Detlaser

polarimetrybeam

aperture

PREX-II n y y

CREX y y n y

MOLLER y y y y y y

SOLID PVDIS y y y y y y

PREX-I Results

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Integrating Photon detectionHAPPEX+PVDIS+PREX experience(CMU, JLab, Syracuse, UVa)

Preliminary Results from Integrating Compton Photon Polarimetry in Hall A of Jefferson Lab. , Parno et al., J.Phys.Conf.Ser. 312 (2011) 052018.

Upgraded photon calorimeter with integrating readout for Hall A Compton Polarimeter at Jefferson Lab., Friend et al., Nucl.Instrum.Meth. A676 (2012) 96-105.

An LED pulser for measuring photomultiplier linearity., Friend et al., Nucl.Instrum.Meth. A676 (2012) 66-69.

Comparison of Modeled and Measured Performance of GSO Crystal as Gamma Detector, Parno et al., in preparation.

HAPPEX-II Results

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e- det: 0xing-Compton Edge self-calibration

Analyzing Power calibration

fit rate for one Energy point

Fit 0xing for one energy point

Laser Polarization

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Determining Laser PolarizationTransfer function translates measured transmitted polarization after cavity to the Compton Interaction Point

Do we know the polarization inside the cavity by monitoring the transmitted light?

Are there effects from ✓vacuum stress✓resonant depolarization✓power level (heating)✓alignment variations?✓model dependence of TF?

Current uncertainty: 0.35%-1%

Very High Precision will require significant improvements. Goal = 0.2%7

Vacuum / Assembly Stress Induced BirefringenceTransfer(Function(not(Constant(� Takes(days(and(hundreds(of(

careful(measurements(� Set(up(known(states(of(light(

in(cavity(and(measure(them(inside(and(in(the(exit(station(

� Fit(data(to(find(transfer(matrix(

� Automated(data(collection(saves(us(hours(

� The(TF(changed(when(we(tightened(the(bolts(on(the(vacuum(flanges(near(the(windows(and(when(we(pulled(vacuum.(

� How(accurate(is(our(TF(now?((

10(

QWP(Angle((deg)(

Circular(Polarization((%

)(

Circular(Polarization(vs(QWP(Angle((

760(Torr(

200(Torr(

10M6(Torr(

Qweak in Hall C

Measurement at exit changes with vacuum pressure. Is it a change on input? Output? Who knows?

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Optical Reversibility TheoremMaking'Use'of'Optical'Transport'Symmetry'

� Research'led'by'Mark'Dalton(UVA)'revealed'that'principles'of'optical'reversibility'allow'determination'of'cavity'DOCP'by'measuring'polarization'of'reflected'light'

� Reflected'circularly'polarized'light'is'blocked'by'the'isolator'and'is'dumped'while'residual'linear'polarization'is'transmitted'and'measured'by'the'photodiode'

� M��������������������� �������photodiode'maximizes'DOCP'at'cavity''

� Addition'of'a'HWP'allows'the'setup'of'any'arbitrary'polarization'state'so'that'we'can'produce'~100%'circularly'polarized'light'at'the'cavity.'

� Later'found'a'publication'detailing'the'use'of'this'technique'for'remote'control'of'laser'polarization.'

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Beam polarization is used for optical isolation: back-reflected circular light is opposite handedness, and is opposite to initial linear polarization after the QWP

This provides a technique to repeatably maximize circular polarization, even in the case of changing intermediary birefringent elements (vacuum or thermal stress, etc.)

This isolation fails, to the degree that light is not perfectly circular at the reflecting surface.

Mark Dalton

This technique appears in the literature as well, for similar configurations (“Remote control of polarization”)

mirror bounces, vacuum windows

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Direct Test of Optimizing Circular Polarization

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Return power (through isolator)

Measurements while scanning over initial polarization set by QWP and HWP.

DoCP in (open) cavity

Excellent agreement

If minimizing return power, maximizing

DoCP at 99.9%+*

Direct Test of Optimizing Circular Polarization

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Return power (through isolator)

Measurements while scanning over initial polarization set by QWP and HWP.

DoCP in (open) cavity

Excellent agreement

If minimizing return power, maximizing

DoCP at 99.9%+*

Fitting Entrance Function

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Measurements while scanning over initial polarization set by QWP and HWP.

DoCP in (open) cavity

Return power, then fit to (simple) optical model

FitMeasured

relates to DoCP

Fitting Entrance Function

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Measurements while scanning over initial polarization set by QWP and HWP.

DoCP in (open) cavity

DoCP from fit to (simple) optical model

Fit DoLPFit DoCP

Measurement at 0.1% level in DoCP from external measurements

Fitting Entrance Function

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Measurements while scanning over initial polarization set by QWP and HWP.

DoCP in (open) cavity

DoCP from fit to (simple) optical model

Fit DoLPFit DoCP Residuals:

measured vs. fit

Measurement at 0.1% level in DoCP from external measurements

Electron beam aperture

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Existing Compton Interaction RegionCollimators protect optics at small crossing angles... but at the cost of larger backgrounds?

Typical “good” brem rate: ~ 100 Hz/uAResidual gas should be about 10x less

How much larger will the halo and tail be, due to synchrotron blowup and the small CEBAF magnetic apertures?

~3.6 degrees puts aperture at size of beampipe, Laser luminosity drops by a factor of 3, but with

9kW this should still be sufficient. Which gives better accuracy?

UPTIME and PRECISION will go up if we use larger apertures (and therefore larger crossing angles)

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Distance from primary beam [mm]0 1 2 3 4 5 6

Anal

yzin

g Po

wer

[%]

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

Analyzing Power, 1.00 GeV and 532 nm

Distance from primary beam [mm]0 1 2 3 4 5 6

Anal

yzin

g Po

wer

[%]

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

PREX

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Distance from primary beam [mm]0 2 4 6 8 10 12

Anal

yzin

g Po

wer

[%]

-2

0

2

4

6

8

Analyzing Power, 2.20 GeV and 532 nm

Distance from primary beam [mm]0 2 4 6 8 10 12

Anal

yzin

g Po

wer

[%]

-2

0

2

4

6

8

CREX

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HAPPEX

18Distance from primary beam [mm]0 2 4 6 8 10 12

Anal

yzin

g Po

wer

[%]

-1

0

1

2

3

4

5

Analyzing Power, 3.00 GeV and 532 nm

Distance from primary beam [mm]0 2 4 6 8 10 12

Anal

yzin

g Po

wer

[%]

-1

0

1

2

3

4

5

1024

Distance from primary beam [mm]0 5 10 15 20 25 30

Anal

yzin

g Po

wer

[%]

-5

0

5

10

15

20

Analyzing Power, 6.60 GeV and 532 nm

Distance from primary beam [mm]0 5 10 15 20 25 30

Anal

yzin

g Po

wer

[%]

-5

0

5

10

15

20

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Distance from primary beam [mm]0 10 20 30 40

Anal

yzin

g Po

wer

[%]

-5

0

5

10

15

20

25

30

Analyzing Power, 11.00 GeV and 532 nm

Distance from primary beam [mm]0 10 20 30 40

Anal

yzin

g Po

wer

[%]

-5

0

5

10

15

20

25

30

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High Precision Goals

correlated

uncorrelated

Participants from UVa, Syracuse, JLab, CMU, ANL, Miss. St., W&M

Independent detection of photons and electrons provides two (nearly) independent polarization measurements;

each should be better than 0.5%

Rela%ve  Error  (%) electron photonPosi%on  Asymmetries -­‐ -­‐Ebeam  and  λlaser 0.03 0.03Radia%ve  Correc%ons 0.05 0.05Laser  Polariza%on 0.20 0.20Background/Dead%me/Pileup 0.20 0.20

Analyzing  Power  Calibra%on  /  Detector  Linearity 0.25 0.35

Total 0.38 0.45

What’s been achieved: ~1% (HAPPEX-3, PREX, Qweak)

Primary Challenges:• Laser Polarization• Synchrotron Light• Signal / Background

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GSO Photon Detector

(&C#$134%/5#D04*57%'*-&'+75/%'*-4#*>#5/1201#.134%/542 3MNO#(0) '-.'=0-%#,9*%*-4P!HO#,9*%*#050.%1*-Q#R0) =0,*4'%0=

S0%%01#%*#740#.90/,01T#@'2201#.134%/5U##:0/=V25/44U

G"5?(+�7*'#/�'&7�(+&8%A

G"5?(+�(+&8%A

=H*;%*&8�E�>#�7*'#/�H�,C�>#

G"5?(+�7*'#/

Existing detector: GSO scintillating crystal,

15cm long, 6cm diameter~60ns, ~150 photoelectron/MeV

Something larger needed to contain showers at high energy, (maybe 6”x6”x15”)

Lead tungstate? Other scintillating or Cerenkov detector? Options exist: simulation and tests needed.

Large GSO detector would be $$$

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