1. Polarimetry Strategy 2. Møller Polarimeter 3. Compton Polarimeter 4. Summary

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Clyde Newman
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1 Vladas Tvaskis (University of Manitoba) Hall C Users Meeting January 202. Polarimetry Strategy 2. Møller Polarimeter 3. Compton Polarimeter 4. Summary

2 Q Weak requires measurement of the beam polarization to dp/p = % Which leads to a contribution to the uncertainty on dq Weak /Q weak of.5% Global strategy for achieving % polarimetry. Use existing Hall C Møller polarimeter to measure absolute beam polarization to <% at low beam currents 2. Use new Compton polarimeter to provide continuous, nondestructive measurement of beam polarization Periodic tests in which Møller and Compton run simultaneously will be used to provide the absolute cross-check of the polarimetry 2 Hall C Meeting, 202

3 . Use existing Hall C Møller polarimeter to measure absolute beam polarization to <% at low beam currents Partially successful Møller successfully re-commissioned, but problems with Q3, occurring coincidentally near large change in polarization due to cathode reactivation; may lead to larger systematic error (pass-). Looks fine for Pass Use new Compton polarimeter to provide continuous, non-destructive measurement of beam polarization Initial results with photon detector are problematic due to glowing CsI Replacement lead-tungstate yields reasonable asymmetries. Result with electron detector provides good mesurements (Pass-, Pass-2) Compton gave us early additional clue that Møller had trouble Electron detector analysis looks very robust data from spring may result in <% systematic errors 3 Hall C Meeting, 202

4 Online results corrected values are coming soon 4 Hall C Meeting, 202

5 In spring, noticed Møller tune not always reproducible quad cycling did not help Rates also somewhat erratic Nominal = 6 khz/ma, sometimes as low as 2 khz/ma 5 Hall C Meeting, 202

6 Diagnosis during 6 MSD revealed short in one set of coils POISSON simulations underway to model effect of bad coil 2D map inserted in Møller simulation Analyzing power is affected polarization will need correction Problem resolved for Run-2 by swapping in spare quad Bad coil 6 Hall C Meeting, 202

Predicted systematic error budget for Q Weak with new Møller configuration low current running only applies to a particular

57% Final value for Run is still under investigation: Preliminary estimate between % and.8% For Pass-2, 0.

5 mr 0.02 Beam direction y 0.5 mr 0.0 Q current 2% 0.0 Q2 current % 0.7 Q2 position mm 0.8 Multiple Scattering 0% 0.

7 Predicted systematic error budget for Q Weak with new Møller configuration low current running only applies to a particular measurement, not polarization for the experiment dp/p = 0.57% dp/p > 0.57% Final value for Run is still under investigation: Preliminary estimate between % and.8% For Pass-2, 0.57 % is achievable Source Uncertainty dasy./asy. (%) Beam position x 0.5 mm 0.32 Beam position y 0.5 mm 0.02 Beam direction x 0.5 mr 0.02 Beam direction y 0.5 mr 0.0 Q current 2% 0.0 Q2 current % 0.7 Q2 position mm 0.8 Multiple Scattering 0% 0.0 Levchuk effect 0% 0.20 Collimator positions 0.5 mm 0.06 Target temperature 50% 0.05 B-field direction 2 o 0.4 B-field strength 5% 0.03 Spin polarization in Fe 0.25 Elec. D.T. 00% 0.04 Solenoid focusing 00% 0.0 Total Hall C Meeting, 202

8 In Compton polarimetry, polarized photons from a laser are scattered from polarized electrons in the electron beam. Scattering rates measured in electron and photon detectors determine the cross-section asymmetry and hence polarization. Laser: External green laser. e - beam passes directly through the cavity. Gain of about 00 gives Watts of power in the cavity (pass-) Scattered electron will be detected in the electron detector. (diamond strip tracker). Independent single-arm measurement of Polarization. Calibration of photon detector (coincidence mode). The ultimate goal in precision on Compton is % systematic error on absolute polarization determination and % statistical error determination per hour. 8 Hall C Meeting, 202

During Run-, used lowest reflectivity mirrors in FP cavity Locked cavity image Gain ~ 00 x 8 Watts into cavity = 700-800 Watts stored

cavity performance is pretty good Late in run, some issues with cavity lock stability Fabry-Perot cavity power vs.

9 During Run-, used lowest reflectivity mirrors in FP cavity Locked cavity image Gain ~ 00 x 8 Watts into cavity = Watts stored power Run-2 use higher R mirrors stored power = Watts FP cavity lock cycled on and off for background subtraction Overall cavity performance is pretty good Late in run, some issues with cavity lock stability Fabry-Perot cavity power vs. time Unclear if this was related to laser itself, or back-reflected light We have swapped in spare laser locking looks pretty robust so far 9 Hall C Meeting, 202

10 With new techniques (using reflected light) we believe we can get close to 00% laser polarization in the cavity. Measurements taken during last April show variations at the 0.05% level We measure it outside the cavity weekly and will use a measured Transfer Function to calculate the intracavity circular polarization Work is underway to get this systematic error as small as possible since it is common to the photon and electron detectors For pass- syst. error for laser polarization is ~ % Polarization after cavity (DOCP - degree of circular polarization) 0 Hall C Meeting, 202

Photon detector operates in energyweighted integrating mode with no threshold Initially, used undoped CsI detector from MIT-Bates Compton Raw asymmetry was about a factor of 3 too small! A~0.

11 Photon detector operates in energyweighted integrating mode with no threshold Initially, used undoped CsI detector from MIT-Bates Compton Raw asymmetry was about a factor of 3 too small! A~0.6%, we expected closer to 2% Borrowed Hall A GSO detector: asymmetries close to 2% Problem attributed to phosphorescence in CsI affects background subtraction and possibly raw asymmetry calculation Hall C Meeting, 202

Hall A GSO detector worked well, but they needed it back Installed existing lead-tungstate prototype in mid-april Lead-tungstate yielded reasonable asymmetries indicating no pathologies

12 Hall A GSO detector worked well, but they needed it back Installed existing lead-tungstate prototype in mid-april Lead-tungstate yielded reasonable asymmetries indicating no pathologies Lead-tungstate is being used for Run 2 Cooling system will improve resolution LED system to monitor linearity (for PMT and Detector) System nearly ready for installation (End of January Beg. Of February) 2 Hall C Meeting, 202

cm Thickness of the Detector 500 μm Strip Pitch 200 μm Offset from Beam 5 mm (~4-8 mm) Rotation Angle ~ 0 o Number of planes 4 Distance

13 Independent single-arm measurement of Polarization. Calibration of photon detector (coincidence mode). Width of Active Area 2. cm Height of Active Area 2. cm Thickness of the Detector 500 μm Strip Pitch 200 μm Offset from Beam 5 mm (~4-8 mm) Rotation Angle ~ 0 o Number of planes 4 Distance Between planes cm 96 strips per plane Metallization: TiPtAu We use pc-cvd (polycrystalline chemical vapour deposition) diamond from Element Six, UK Gain is 20 mv/fc, threshold is mv and the average charge collection is 9000 electrons. 3 Hall C Meeting, 202

14 Electron detector: 4 planes, diamond strip detector Pitch = 200 mm Typical operational mode integrates hits in a single strip over a full helicity window Quasi-tracking based trigger reduces backgrounds Normalized yield Run- issues Flex cables connecting planes to amplifier-discriminators not optimal resulting in smaller signal Amplifier-discriminator manufacturing issues led to lots of noise, requiring high thresholds Result somewhat non-uniform spectra 4 Hall C Meeting, 202

Detector planes installed using traveling microscope with a near-zero offset New Flex Cables with smaller

Higher power laser would improve the statistic (~2x) in the same run-time.

Wider threshold range available on QWADs which are also remotely controllable.

15 Detector planes installed using traveling microscope with a near-zero offset New Flex Cables with smaller capacitance ~50 pf (old cables ~ 200 pf). Signal increased by factor ~2. Higher power laser would improve the statistic (~2x) in the same run-time. New version (3) of QWADs has better shielding from noise and does not have any inter-channel correlation. Wider threshold range available on QWADs which are also remotely controllable. New design has 8 layers Individual RF shields cover analog part of each channels Additional capacitors included (on board s power lines) to improve stability against digital noise. 5 Hall C Meeting, 202

16 Input Parameters Beam Energy (E beam ) Laser Wavelength (λ) Magnetic Field (F) Chicane bend angle (θ bend ) Value.59 GeV 532 nm T 0.3 deg D Max D 0.2 Par. SN 6 Hall C Meeting, 202

17 A P e N N Aexp P A exp l N N P P A e l Calculation of polarization requires Laser off - Background Electronic noise Theory (Asymmetry) Laser Polarization 7 Hall C Meeting, 202

Syst. Error due to Value (%) Size of the Strip 0.2 2 Strip Separation 0.35 3 Difference between planes 0.2 4 Magnetic Field (Abs. Value) 0.05 5 Magnetic Field (F.

18 Syst. Error due to Value (%) Size of the Strip Strip Separation Difference between planes Magnetic Field (Abs. Value) Magnetic Field (F. Field)? (MC) 6 Dead Time? (very small) 7 Charge Asymmetry Beam/Laser Position? (MC) 9 Laser Polarization 0.4 (very preliminary) 0 TBD? TOTAL: Hall C Meeting, 202

Edet Data - shown from 0/04/20 till 2/05/20 Each Point

photocathode) Solid line re-activation Time = Total time

19 Edet Data - shown from 0/04/20 till 2/05/20 Each Point represents a Run (~h) Each Run = 2-5 sub-runs Statistical Errors ~ % for Good Runs Stat. and Full Errors are shown dotted lines spot changes (on photocathode) Solid line re-activation Time = Total time of the run when Laser and Beam are ON. Beam Current ~60 μa Trigger 2/3 9 Hall C Meeting, 202

20 Edet Data - shown from 0/04/20 till 2/05/20 Each Point represents a Run (~h) Each Run = 2-5 sub-runs Statistical Errors ~ % for Good Runs Stat. and Full Errors are shown dotted lines spot changes (on photocathode) Solid line re-activation Time = Total time of the run when Laser and Beam are ON. Beam Current ~60 μa Trigger 2/3 20 Hall C Meeting, 202

21 Edet Data - shown from 26//20 till 4/2/20 Each Point represents a Run (~h) Each Run = 2-7 sub-runs Statistical Errors ~ 0.5 % for Good Runs Stat. and Full Errors are shown dotted lines spot changes (on photocathode) Solid line re-activation Time = Total time of the run when Laser and Beam are ON. Beam Current ~60 - ~70 μa Trigger 2/4 2 Hall C Meeting, 202

22 22 Hall C Meeting, 202

23 Continue taking data Preliminary ( st level online analysis) results Work on Syst. Errors Install LED system for Photon Detector Final Analysis/Results Alphabetical List College of William and Mary, Jlab, Mississippi State University, MIT Bates, TRIUMF, University of Manitoba, University of Virginia, University of Winnipeg, Yerevan Physics Institute. 23 Hall C Meeting, 202

24 24 Hall C Meeting, 202

25 25 Hall C Meeting, 202 Input Parameters Value Beam Energy (E beam ).59 GeV Laser Wavelength (λ) 532 nm Magnetic Field (F) T Chicane bend angle (θ bend ) 0.3 deg a a d d a r A a a a a a r d d l e l e P A A P P P A N N N N A exp exp Output Parameters Value Asymmetry at Compton Edge Max. Electron Displacement (m) e - Displacement at Asymmetry 0 (m) Max. Scattered Photon Energy (GeV) Photon Energy at Asymmetry 0 (GeV)

26 Hall C Meeting, 202

27 27 Hall C Meeting, 202

Inputs: V E b =.59 GeV λ = 532.0 nm Θ b = 0.3 o Mag F =0.544 T d =.25 m L det =.645 m M T L X K X 2 R = 7.

28 Inputs: V E b =.59 GeV λ = nm Θ b = 0.3 o Mag F =0.544 T d =.25 m L det =.645 m M T L X K X 2 R = m R / = m θ / = degree X = m X 2 = m X 0 = m Max Displacement = m Disp. at Asum 0 = m 28 Hall C Meeting, 202 K L Lsin K d det tg h b b Lcos L det R h b b K tg R M cos h b R h cosb M d M sin sin x d M sinb cos b b tg Rtg b d tg h K d M b b h b K R h : M / x / L det / R tg / tg d R h / d / tg / / 2 h K

Electron Beam Polarimetry at JLab Hall C Dave Gaskell PST 2009 September 7, 2009

Electron Beam Polarimetry at JLab Hall C Dave Gaskell PST 2009 September 7, 2009 1. Møller Polarimeter 2. Compton Polarimeter 3. Summary JLab Polarimetry Techniques Three different processes used to measure