Compton polarimetry for EIC

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

ERHIC 50 mA injector using several sources 14 to 55 MHZ Energy Recovery Linac Up to 5 pass

Compton asymmetry

MEIC Storage ring MHz = 1.33 ns bunch structure 3 A at 3 GeV and 180 mA at 11 GeV Macrobunch with one polarization 3.7 us

Hall A Compton chicane layout

Hall A perot fabry cavity

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

Hall A Photon detector FADC readout SIS MHz FADC Digital integration

Happex III results Upgraded photon calorimeter with integrating readout for Hall A Compton Polarimeter at Jefferson Lab Friend Nucl.Instrum.Meth. A676 (2012) Friend Phd Thesis CMU 2012

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

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

Preliminary Systematic Uncertainties Systematic UncertaintyUncertainty ΔP/P (%) Laser Polarization 0.1%0.1 Dipole field strength ( 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

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

Compton EIC requirements High radiation hardness High counting rates

Electron detector proposal Quartz integrating detector

Diamond strip

Micromegas based c

Testing method

Roman pot

To do

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