Compton polarimetry for EIC Jefferson Lab Compton Polarimeters

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

MEIC Storage ring MHz = 1.33 ns bunch structure 3 A at 3 GeV and 180 mA at 11 GeV Macrobunch with one polarization 2.3 us

Compton asymmetry

Synchrotron Radiation Parameters F. Lin--- Beam energyGev Beam current A Total SR power MW Linear SR power density kW/m Energy loss per turn MeV Energy spread Longitudinal damping time ms

Compton rates Green laser, 1.3 degree crossing angle 350 um electron beam EnergyRate (Hz/W/A)

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) Phd Thesis Syracuse

Hall A Photon detector FADC readout SIS MHz FADC Digital integration

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

Compton EIC requirements High radiation hardness High counting rates Laser power

Simulation background Bremstrahlung Halo Photon detector Electron detector With apertures No apertures 1 KW power

Electron detector proposal Quartz integrating detector PREX type Pure Cerenkov detector Integrated at GHz rates PMT

Strip detector Diamond or Micromegas c

Hall A Electron detector chamber

Testing method Usual Compton High rates in beam low current, generate beam charge asymmetry to measure Straight beam low current Chicaned beam High current Compton electrons

To do Refine simulation background Evaluate RF Test radiation hardness and rate capability Test Integrated method Evaluate effect of windows on measurement in simulation and in beam

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