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The A2 recoil nucleon polarimeter

The A2 recoil nucleon polarimeter. Daniel Watts University of Edinburgh, UK. q. Why nucleon polarimetry?. Would add a unique capability to the MAMI setup – Valuable compliment to circularly and linearly polarised photon beams and polarised target systems.

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The A2 recoil nucleon polarimeter

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  1. The A2 recoil nucleon polarimeter Daniel Watts University of Edinburgh, UK q

  2. Why nucleon polarimetry? • Would add a unique capability to the MAMI setup – Valuable compliment to circularly and linearly polarised photon beams and polarised target systems. • Observables from recoil group will allow MAMI to make the first complete measurement in pion/eta photoproduction (Nucleon polarimetry proposal approved by last MAMI-ELSA PAC)

  3. Double-polarisation in pseudo-scalar meson photoproduction Polarisation of g target recoil Observable

  4. q Nucleon Scattering and polarisation n(q,f) =no(q){1+A(q)[Pycos(f)–Pxsin(f)] Number of nucleons scattered In the direction q, f x and y (transverse) components of nucleon polarisation Polar angle distribution for unpolarised nucleons Analysing power of scatterer

  5. New GEANT simulations incorporating polarimetry • Simulate p(g,p0)p channel – realistic beam/target & detector parameters • New routines written for GEANT3 – introduced modulation of f for hadronic interactions (take A=1) • All other processes left in. e.g. coulomb scattering, nuclear de-excitations … • Explore possible designs for polarimeter p0 g q p p/ gxp defines f=0 plane

  6. Design 1: Graphite at CB exit CB skirt A = (s+- s-)/ (s++ s-) ~32% reduction in A epol ~ 2.4% (Eg=0.3-0.6 GeV, qscat>20) Target Reconstructed Phi in incident nucleon frame (deg) Graphite scatterer TAPS Analyser efficiency (7cm graphite) qp(cm) > 130 Yield (a.u) Yield (a.u) Qp(COM) (Deg) Eg(MeV)

  7. Design 2: Graphite in CB tunnel A = (s+-s-)/ (s+-s-) ~45% reduction in A epol ~ 3% (Eg=0.3-0.6 GeV, qscat>15) Graphite scatterer Target Reconstructed Phi in incident nucleon frame (deg) qp(cm) > 130 Analyser efficiency (7cm graphite) Yield (a.u) Yield (a.u) Qp(COM) (Deg) Eg(MeV)

  8. Design 3: Graphite Near Target A = (s+-s-)/ (s+-s-) ~46% reduction in A epol ~ 3 % (Eg=0.3-0.6GeV, qscat>15) Target Graphite scatterer Reconstructed Phi in incident nucleon frame (deg) Analyser efficiency (7cm graphite) qp(cm) > 90 Yield (a.u) Yield (a.u) Qp(COM) (Deg) Eg(MeV)

  9. Design 4: Graphite Near Target + subsequent CB detection!! A = (s+-s-)/ (s+-s-) ~53% reduction in A epol ~ 2.6% (Eg=300-600 MeV, qscat>20) Graphite scatterer Reconstructed Phi in incident nucleon frame (deg) Target Analyser efficiency (7cm graphite) qp(cm) > 60o Yield (a.u) Yield (a.u) • ~35% dilution of analysing power • Acceptance X% • If proves worth can move more upstream to greatly increase acceptance Qp(COM) (Deg) Eg(MeV)

  10. Test polarimeter • Polarimeter with adjustable thickness and hole diameter • Will fit in “orange pipe” used in PID tests • Polarimeter presently being machined in Edinburgh • Ready for use in tests from late Oct

  11. Tracker detector(s) • First polarimetry measurements on proton target do not need tracker – BUT tracker necessary for neutron target measurements (Fermi motion) • Need to finalise polarimeter design before can finalise tracker design – need test beam time Tracker Possibilities - Si detectors on face(s) of graphite - Wire chambers - Scintillating fibre • Money already available – Edinburgh £120k GWU £50k Also Mainz, UCLA , …

  12. Conclusion • Simulations give good indication that we can start testing nucleon polarimeter (and getting first data!) now. • Test polarimeter module ready this month - need test beamtime with prototype to move the project forward • Forward angle tracker pre-requisite to allow neutron target measurements in the longer term

  13. Design 4: Graphite Near Target + subsequent CB detection!! A = (s+-s-)/ (s+-s-) ~50% reduction in A epol ~ X% Reconstructed Phi in incident nucleon frame CB tunnel Graphite qp(cm) > 60 • ~35% dilution of analysing power • Acceptance X% • If proves worth can move more upstream to greatly increase acceptance Egamma (MeV)

  14. Design 1: Graphite at CB exit A = (s+-s-)/ (s+-s-) ~32% reduction in A epol ~ 2.4% Reconstructed Phi in incident nucleon frame CB tunnel Graphite qp(cm) > 130 Egamma (MeV)

  15. Design 3: Graphite Near Target A = (s+-s-)/ (s+-s-) ~46% reduction in A epol ~ X % Reconstructed Phi in incident nucleon frame CB tunnel Graphite • ~35% dilution of analysing power • Acceptance X% • If proves worth can move more upstream to greatly increase acceptance Egamma (MeV)

  16. Design 2: Graphite in CB tunnel CB tunnel Graphite A = (s+-s-)/ (s+-s-) ~35% reduction in A epol ~ 3% Reconstructed Phi in incident nucleon frame qp(cm) > 130 Egamma (MeV)

  17. Nucleon polarimetry concept Useful scattered event Select events with scattering angles larger than ~10 degrees : arising from nuclear interaction Hydrogen target cell g beam TAPS Graphite sheet Crystal Ball n(q,f) =no(q){1+A(q)[Pycos(f)–Pxsin(f)]

  18. Design 3 – 7cm Graphite 8cm from target A = (s+-s-)/ (s+-s-) Reconstructed Phi in incident nucleon frame • ~30% dilution of analysing power • Acceptance X% • If proves worth can move more upstream to greatly increase acceptance Egamma (MeV)

  19. Previous experimental data – SAID database P T Data for all CM breakup angles Ox’ Cx’ Recent JLAB data not in database

  20. GEANT simulation of polarimeter • Simulation includes realistic • smearing of energy deposits due to experimental energy resolution • and proper cluster finding algorithms • Finite target size and Eg resolution included No Graphite With Graphite scatterer Angle between qN(Eg,qp) and TAPS hit

  21. Design 1: Graphite in CB tunnel A = (s+-s-)/ (s+-s-) Reconstructed Phi in incident nucleon frame CB tunnel Graphite • ~30% dilution of analysing power • Acceptance X% Egamma (MeV)

  22. qp(CM) >~130o Kinematic acceptance of polarimeter p(g,p)N Polarimeter acceptance Pion angle in CM (deg) Eg=150 MeV Eg=200 Eg=300 Eg=500 Eg=750 Eg=1000 Eg=1500 Nucleon angle in lab (deg)

  23. More forward recoils than for pion production. Almost all recoils are incident on polarimeter up to ~0.8 GeV Kinematic acceptance of polarimeter p(g,h)N Polarimeter acceptance CM h angle (degrees) Eg=720 Eg=820 Eg=920 Eg=1520 Lab nucleon angle (degrees)

  24. MAID predictions and expected data accuracy - p(g,p)N 300 hrs MAMI B 500 hrs MAMI C

  25. New GEANT simulations • Simulate New routines added to GEANT – introduced f modulation for hadronic interactions (take A=1) • Simulated p(g,p)p0 data. Run through AcquRoot analysis. Accurate description of target size, beam properties, CB & mini TAPS. Eg=300-600 MeV • All other processes left in. • Explore possible designs for polarimeter without need for tracker p

  26. MAID predictions and expected data accuracy - p(g,p)N 300 hrs MAMI B Full MAID No P11(1440)

  27. Cx’ – Extraction and expected accuracy Cx’ 0 180 360 Photon energy (MeV) - • Pg=0.7, Eg=±25MeV, qp=130±10 • s ~ 1 mb/sr →DCx ~ 0.015 • s ~ 0.1 mb/sr →DCx ~0.05 • Greatly improved data quality Plot difference in f distributions for two helicity states (cut on region of q with reasonable A(q)) Left with simple sin(f) Dependence. Extract Px

  28. Expected data accuracy Common parameters: Photon beam: 2.5x105g sec-1 MeV-1 Bin ±12.5 MeV Target: 2.11023 nuclei / cm2 Meson: e(p0) = 80% e(h) = 35% Bin ±10o Polarimeter: 3% probability for a (detected) nuclear scatter Average analysing power ~0.4

  29. Principles of nucleon polarimetry • Well established technique – relies on spin-orbit interaction in Nucleon-Nucleon interaction • Polarimeters - exploited nucleon or nuclear targets (2H, 4He, 12C, 28Si) – tended to use materials with well known analysing powers A1 FPP Kent state GEn Polarimeter pomme

  30. qscat Polarimetry basics • Measure direction of nucleon before and after the scatterer with sufficient accuracy to determine an analysing reaction has taken place. For incident protons also have multiple (coulomb) scattering Qscat=5-20o

  31. Scattered nucleon detection in TAPS • 1 TAPS block ~ position resolution for hit • TAPS~0.9m from scatterer N Straight through 10o scatter 20o scatter p

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