Compton polarimetry for EIC Jefferson 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 Ptitsyn eRHIC Accelerator Design EIC2014

MEIC Storage ring – Ring ring 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 with horizontal beam crossing Injector 12 GeV CEBAF Pre-booster SRF linac Ion source Cold GeV/c proton collider ring Three Figure-8 rings stacked vertically Electron cooling

Compton asymmetry e +  e’ +  ’ (( ) (( )

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 SIS MHz FADC Digital integration with 240 Hz helicity flip Record all the signal for a given helicity Compute integrated asymmetry for a pair

Happex III results Friend Nucl.Instrum.Meth. A676 (2012) Friend Phd Thesis CMU 2012 Pe =89.41%

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

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

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

Simulation background Bremstrahlung Halo 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-Q 2 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 Electron tracking detector Photon calorimeter Possible implementation in low Q 2

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