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Compton polarimetry for EIC
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Outline Polarized electron beam Compton process Compton polarimeters at Jefferson Laboratory – Parity experiments at Jlab : PREX, Qweak, PVDIS, Moller – Diamond electron detector – Hall A GSO crystal : integrated method – Hall A perot fabry cavity ERHIC MEIC Background studies Detector requirements Detector proposals
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ERHIC 50 mA injector using several sources 14 to 55 MHZ Energy Recovery Linac Up to 5 pass
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Compton asymmetry
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MEIC Storage ring 748.5 MHz = 1.33 ns bunch structure 3 A at 3 GeV and 180 mA at 11 GeV Macrobunch with one polarization 3.7 us
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Hall A Compton chicane layout
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Hall A perot fabry cavity
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Cavity power Green laser using IR seed laser and PPLN frequency doubling Around 5 KW power 10 KW reachable Abdurahim Rakhman (2011) Ms Thesis Syracuse
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Hall A Photon detector FADC readout SIS3320 250 MHz FADC Digital integration
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Happex III results Upgraded photon calorimeter with integrating readout for Hall A Compton Polarimeter at Jefferson Lab Friend Nucl.Instrum.Meth. A676 (2012) 96-105 Friend Phd Thesis CMU 2012
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Hall C Compton Electron Detector Diamond 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
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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
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Preliminary Systematic Uncertainties Systematic UncertaintyUncertainty ΔP/P (%) Laser Polarization 0.1%0.1 Dipole field strength (0.0011 T)0.02 Beam energy 1 MeV0.09 Detector Longitudinal Position 1 mm0.03 Detector Rotation (pitch) 1 degree0.04 Asymmetry time averaging 0.15% Asymmetry fit 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
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Polarization Measurements Q-Weak Run 2 – November 2011 to May 2012 P Moller +/- stat (inner) +/- point-to-point systematic (0.54%) P Compton +/- stat +/- preliminary systematic (0.6%) Photocathode re-activation 0.64% normalization unc. not shown Preliminary
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Compton EIC requirements High radiation hardness High counting rates
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Electron detector proposal Quartz integrating detector
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Diamond strip
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Micromegas based c
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Testing method
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Roman pot
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To do
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Conclusion Jefferson Lab ideal ground for Compton testing – Photon detector – Electron detector Need for – Radiation hard detector – High rate : integrated Possible upgrade of setup for electron detector testing
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