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Compton polarimetry for EIC Jefferson Lab Compton Polarimeters.

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Compton polarimetry for EIC Jefferson Lab Compton Polarimeters
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Compton polarimetry for EICJefferson Lab Compton Polarimeters

ERHIC• 6.6 GeV to 21.2

GeV • 9.4 MHz Repetion

rate• Up to 21

recirculations• 50 mA with

“gatling gun” design

• 80 % min polarization

• Similar to CEBAF

Vadim PtitsyneRHIC Accelerator DesignEIC2014

MEIC

• Storage ring – Ring ring• 748.5 MHz = 1.33 ns bunch

structure• 3 A at 3 GeV and 180 mA at 11

GeV• 2 macrobunch with one

polarization 2.3 us• Measure polarization average

of the two macrobunch• Every electron bunch crosses

every ion bunch

Warm large booster(up to 25 GeV/c)

Warm 3-12 GeV electron collider ring

Medium-energy IPs withhorizontal beam crossing

Injector

12 GeV CEBAF

Pre-boosterSRF linac Ion

source

Cold 25-100 GeV/cproton collider ring

Three Figure-8 rings stacked vertically

Electron cooling

Compton asymmetrye + g e’ + g’

s( ) e + g e’ + g’

s( )

)

Hall A Compton chicane

Cavity power

• Green laser using IR seed laser and PPLN frequency doubling

• Around 5 kW power

• 10 kW reachable

• Lazer polarization flip

• Abdurahim Rakhman (2011) Phd Thesis Syracuse

Hall A Photon detector • FADC readout SIS3320 250 MHz FADC• Digital integration with 240 Hz helicity flip• Record

all thesignalfor a givenhelicity

• Compute integratedasymmetryfor a pair

Happex III resultsFriendNucl.Instrum.Meth. A676 (2012) 96-105

Friend Phd Thesis CMU 2012

Pe =89.41%

Hall C Compton Electron DetectorDiamond microstrips used to detect scattered electrons Radiation hard Four 21mm x 21mm planes each with 96 horizontal 200 μm wide micro-strips. Rough-tracking based/coincidence trigger suppresses backgrounds

Compton Electron Detector Measurements

Polarization analysis: Yield for each electron helicity state

measured in each strip Background yields measured by

“turning off” (unlocking) the laser Asymmetry constructed in each strip

Strip number corresponds to scattered electron energy Endpoint and zero-crossing of

asymmetry provide kinematic scale

2-parameter fit to beam polarization and Compton endpoint

Polarization MeasurementsQ-Weak Run 2 – November 2011 to May 2012

PMoller +/- stat (inner) +/- point-to-point systematic (0.54%)

PCompton +/- stat +/- preliminary systematic (0.6%)

Photocathode re-activation

0.64% normalization unc. not shown

Preliminary

Preliminary Systematic UncertaintiesSystematic Uncertainty Uncertainty ΔP/P (%)

Laser Polarization 0.1% 0.1Dipole field strength (0.0011 T) 0.02

Beam energy 1 MeV 0.09Detector Longitudinal Position 1 mm 0.03

Detector Rotation (pitch) 1 degree 0.04Asymmetry time averaging 0.15% 0.15%

Asymmetry fit 0.3% 0.3%DAQ – dead time, eff. Under study ??

Systematic uncertainties still under investigation, but final precision expected to be better than 1% DA- related systematics likely the most significant remaining issue to study

Simulation background

BremstrahlungHalo

• 1 kW green laser• 1 A• 3 GeV electron

beam

• Halo contribution modeled on PEP II

Photon detector signal

Electron detector signal

Compton polarimeter in low-Q2 chicane

Same polarization as at the IP due to zero net bend

Non-invasive continuous polarization monitoring

Polarization measurement accuracy of ~1% expected

No interference with quasi real photon tagging detectors

c

Laser + Fabry Perot cavity

e- beam

Quasi-real high-energy photon tagger

Quasi-real low-energy photon tagger

Electrontracking detector

Photon calorimeter

Possible implementation in low Q2

Hall A Compton chicane

Vertical motion of electron detector to move detector close to the beam( up to 5 mm )Photon

detector on movable table

Conclusion

• Compton polarimetry at 1% level achieved at Jefferson Laboratory and aiming at 0.5 % for 12 GeV parity program

• Jefferson Lab ideal ground for Compton testing for EIC since Compton is non invasive– Photon detector testing straight forward– Electron detector testing doable with planning

because of vacuum. Looking into Roman pot option for ease of detector swapping


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