Introduction Polarimeters at MAMI Analysis Future Conclusion. Polarimetry at MAMI. V. Tyukin, Inst. of Nuclear Physics, Mainz, Germany

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1 Polarimetry at MAMI V. Tyukin, Inst. of Nuclear Physics, Mainz, Germany Workshop to Explore Physics Opportunities with Intense, Polarized Electron Beams up to 3 MeV MIT March 213

2 Contents Introduction Polarimeters at MAMI Analysis Looking the source of discrepancy G Future Conclusion

3 XYPMO XY XYPMO XYPMO XYPMO XYPMO XYPMO XY XY XY 2.45 Co li XYPMO XYPMO XYPMO XYPMO XYPMO XYPMO XYPMO XYPMO XYPMO XYPMO XY XY XY F XYPMO XYPMO F XYPMO AMI MAMI Modulatorenhalle A4 Compton polarimeter 1 m A1 Møller Halle A Halle B DSM Halle A2 Moller polarimeter Spektrometer_halle A2 Møller A4 Laser Compton Backscattering B2 Mott B2 Mott polarimeter A1 Moller polarimeter

4 AMI Cathodes 1 of polarized electron source at MAMI Super lattice GaAsP photo cathodes Quantum Efficiency 1% Polarization P 88% Standard cathodes for JLAB, SLAC ant later MAMI, ELSA 1 T. Maruyama et al. Systematic study of polarized electron emission from strained GaAs/GaAsP superlattice photocathodes. In: Applied Physics Letters (24).

5 olarimetrs B2 Mott polarimeter MeVin Halle-A 2 Upper arm (vacuum chamber and magnet yoke cut away) Collimator Target To beam dump Spin direction Lower arm Incoming beam Vacuum window PM Plastic scintillator Asymmetry measurements at a level of <1% relative variation. 29 upgrade by multichannel analyzer 2 V. Tioukine, K. Aulenbacher, and E. Riehn. A Mott polarimeter operating at MeV electron beam energies. In: Review of Scientific Instruments 82.3 (211), p

6 olarimetrs Møller polarimeters A1 Møller polarimeter MeV in spectrometer hall 3 A2 Møller polarimeter MeV in tagger hall 3 Peter Bartsch. Aufbau eines Moeller-Polarimeters für die Drei-Spektrometer-Anlage und Messung der Helizitaetsasymmetrie in der Reaktion p( e, e p)piim Bereich der Delta-Resonanz. ger. PhD thesis. Johannes Gutenberg-Universitaet, 22.

7 aw datas Raw experimental data of A1 and A2 collaborations. 1 A2 at 158 MeV A1 at 158 MeV A1 at 855 MeV 75 5 Polarisation,[%] Angle, [deg]

8 aw datas Measurements of beam polarization Collaboration Polarisation,[%] Remarks SLAC, 1 kev as reference B2, 3.5 MeV ±.51 measured ±.51 corrected A1, 855 MeV 9.17 ±.812 measured A1, 158 MeV 9.99 ±.621 measured A2, 158 MeV ± 1.87 corrected B2 value corrected this presentation later A2 value corrected at.978, chicane Φ = 3.3, Φ 1 = Systematic errors not included

9 ooking the source of discrepancy The search of the true polarization Sherman function calculation is affected by influence of radiative effects. How large? A good question. Could be below.5 %. Extrapolation to foil thickness zero, seems possible below.3 % using power Monte-Carlo simulation. Target induced background, seem to keep below.5 %. This talk.

10 ooking the source of discrepancy B2 Mott experimental Elastic scattering spin down, with target.5*e, with target spin up, with target.5*e, without target, smoothed Bremsstrahlung 1 1 Count per channel with target,[] Preliminary Count without target,[] Channel number, []

11 ooking the source of discrepancy B2 Mott experimental Elastic scattering Count per channel with target,[] spin down, with target.5*e, with target spin up, with target Preliminary.5*E, without target, smoothed Count without target,[] Bremsstrahlung Q 1: The elastic peak has a spin sensitive tail Channel number, []

12 ooking the source of discrepancy B2 Mott experimental Elastic scattering Count per channel with target,[] spin down, with target.5*e, with target spin up, with target Preliminary Channel number, [].5*E, without target, smoothed Count without target,[] Bremsstrahlung Q 1: The elastic peak has a spin sensitive tail. Q 2: The origin a low energy peak is not definitive clear. Photo or/and secondary emission?

13 ooking the source of discrepancy B2 Mott experimental Elastic scattering Count per channel with target,[] spin down, with target.5*e, with target spin up, with target Preliminary Channel number, [].5*E, without target, smoothed Count without target,[] Bremsstrahlung Q 1: The elastic peak has a spin sensitive tail. Q 2: The origin a low energy peak is not definitive clear. Photo or/and secondary emission?

14 ooking the source of discrepancy Back ground definition - Problem description Not possible to separate background electron during beam Background electrons initially scattered on target and moving NOT in detector direction Background electron could reach detectors after multiple secondary processes Software package Geant4 4 be used for simulation S. Agostinelli et al. Geant4 a simulation toolkit. In: NIMA 56.3 (23), pp. 25

15 View of Mott polarimeter in Geant4 simulation All parts and materials included Figure: Electrons -red, gamma rays -purpure

16 View of Mott polarimeter in Geant4 simulation All parts and materials included Presented tracks fulfill a condition, that scattered primary or secondary particle reach detectors Figure: Electrons -red, gamma rays -purpure

17 Dummy volumes - test spheres Gold target Upper dummy volume Primary beam Down dummy volume polarization effect not included, Geant4 became too slow Dummy volumes in Geant4 simulation. step target-dummy spin sensitive (blue) if not background (dashed red line)

18 Dummy volumes - test spheres Gold target Upper dummy volume Primary beam Down dummy volume polarization effect not included, Geant4 became too slow Dummy volumes in Geant4 simulation. step target-dummy spin sensitive (blue) if not background (dashed red line)

19 Simulated Energy Spectrum Polarised count rates,[] Pol tracks, 45 days simulation, 1 ms real life polarized - blue Energy deposit in detector, [MeV]

20 Simulated Energy Spectrum Unpol Energy deposit in detector, [MeV] Unpolarised count rates,[] tracks, 45 days simulation, 1 ms real life unpolarized -lila

21 Simulated Energy Spectrum Polarised count rates,[] Pol Unpol Energy deposit in detector, [MeV] Unpolarised count rates,[] tracks, 45 days simulation, 1 ms real life polarized - blue unpolarized -lila

22 Optical photons in BC4 Scintillator housing PMT cathode G4OpticalPhotons class is used separately. The propagation of optical photons in scintillator increase the width of spectrum. Input beam Photons in scintillator

23 Optical photons in BC4 continue Pol Polarised count rates,[] Energy deposit in detector, [MeV] Simulated spectrum

24 Optical photons in BC4 continue Pol 2 2 Polarised count rates,[] Scintillator housing PMT cathode Energy deposit in detector, [MeV] Input beam Photons in scintillator Simulated spectrum Response of scintillator and PMT depends on impact parameters.

25 Optical photons in BC4 continue 2 Pol 2 spin down, with target.5*e, with target 18 Scintillator housing PMT cathode 1 spin up, with target.5*e, without target, smoothed 1 Polarised count rates,[] Count per channel with target,[] Preliminary Count without target,[] Energy deposit in detector, [MeV] Channel number, [] Input beam Photons in scintillator Simulated spectrum Response of scintillator and PMT depends on impact parameters. Result spectrum should be convoluted with the response.

26 Optical photons in BC4 continue Spin down Spin up G Count per channel,[] 5 Preliminary Count per channel, [a.u.] Leads to good agreemnt Channel number, []

27 Optical photons in BC4 continue Spin down Spin up G Count per channel,[] 5 Preliminary Count per channel, [a.u.] Leads to good agreemnt Channel number, []

28 Remarks to Q.2 Count per channel with target,[] with target Preliminary without target, smoothed Channel number, [] Count without target,[] Not standard operation. Position and magnitude depend on mean energy of spectrometer. Could be usefull???

29 Simulation results Analyzed tracks at HIMSTER 45 days

30 Simulation results Analyzed tracks at HIMSTER 45 days E = Mev collected 3937 only polarized events

31 Simulation results Analyzed tracks at HIMSTER 45 days E = Mev collected 3937 only polarized events E = Mev collected 6592 polarized events while 58 unpolarized events. Relation noise to signal.88%

32 Simulation results Analyzed tracks at HIMSTER 45 days E = Mev collected 3937 only polarized events E = Mev collected 6592 polarized events while 58 unpolarized events. Relation noise to signal.88% Background substitution based on Geant4 simulation. This lead to increase initial beam polarization as follow: ( P = P mess 1 + N ) noise (1) N signal

33 Simulation results Analyzed tracks at HIMSTER 45 days E = Mev collected 3937 only polarized events E = Mev collected 6592 polarized events while 58 unpolarized events. Relation noise to signal.88% Background substitution based on Geant4 simulation. This lead to increase initial beam polarization as follow: ( P = P mess 1 + N ) noise (1) N signal Measured P mess =87.63 corrected up to P =88.41.

34 Simulation results Analyzed tracks at HIMSTER 45 days E = Mev collected 3937 only polarized events E = Mev collected 6592 polarized events while 58 unpolarized events. Relation noise to signal.88% Background substitution based on Geant4 simulation. This lead to increase initial beam polarization as follow: ( P = P mess 1 + N ) noise (1) N signal Measured P mess =87.63 corrected up to P = Q2: Low energy peak. Probably magnet selected photo or/and secondary emission from walls. Not complet included in Geant4.

35 uture Double Mott Polarimeter 5 Original double scattering Mott polarimeter, developed by Kessler, Uni Munster Delivered and installed at test electron source Allows to measure asymmetry with.3 % 5 A. Gellrich and J. Kessler. Precision measurement of the Sherman asymmetry function for electron scattering from gold. In: Phys. Rev. A 43 (1991), pp

36 uture Hydro Møller Project 6 Proposed by E. Chudakov and V. Lupov. See talk E. Chudakov At the moment R & D stage. See talk P. Aguar 6 Luppov V. Chudakov E. Moller polarimetry with atomic hydrogen targets. In: Nuclear Science, IEEE Transactions on 51.4 (8/24), pp

37 Conclusion Mott Polarimeter, Double Scattering Mott Polarimeter and Hydro Møller MAMI or MESA Future theoretical and experimental investigation of Mott polarimeter necessary. Additional independent measurements of polarisation should be provided. Double Scattering Mott Polarimeter - commissioning 213 Hydro Møller Polarimeter - at the moment R& D stage

38 Thank for your attention. Thank for your attention.