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The Longitudinal Polarimeter at HERA

The Longitudinal Polarimeter at HERA. W. Lorenzon (Michigan) Collaboration. Polarization at HERA Laser System & Calorimeter Statistical and Systematic Precision Laser Cavity Project Summary and Outlook. Electron Polarization at HERA. Sokolov Ternov Effect.

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The Longitudinal Polarimeter at HERA

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  1. The Longitudinal Polarimeter at HERA W. Lorenzon (Michigan) Collaboration • Polarization at HERA • Laser System & Calorimeter • Statistical and Systematic Precision • Laser Cavity Project • Summary and Outlook EIC, 8 November 2002

  2. Electron Polarization at HERA EIC, 8 November 2002

  3. Sokolov Ternov Effect EIC, 8 November 2002

  4. HERMES Spin Rotators EIC, 8 November 2002

  5. Principle of the Pe Measurement with the Longitudinal Polarimeter Eg l (2.33 eV) e (27.5 GeV) a Back Scattered Compton photon Calorimeter Compton Scattering: e+lg e’+ Cross Section: ds/dEg = ds0/dEg[1+PePlAz(Eg)] ds0, Az: known (QED) Pe:longitudinal polarization ofe beam Pl: circular polarization (+-1) of laser beam EIC, 8 November 2002

  6. Experimental Setup - Overview EIC, 8 November 2002

  7. Experimental Setup – Laser System EIC, 8 November 2002

  8. Experimental Setup - Details EIC, 8 November 2002

  9. Laser Control - COP EIC, 8 November 2002

  10. Polarimeter Operation I EIC, 8 November 2002

  11. Polarimeter Operation II EIC, 8 November 2002

  12. Polarization Determination EIC, 8 November 2002

  13. Polarization Performance EIC, 8 November 2002

  14. “Non-Intrusive” Method EIC, 8 November 2002

  15. A large Systematic Effect - Solved EIC, 8 November 2002

  16. Systematic Uncertainties EIC, 8 November 2002

  17. New Sampling Calorimeter EIC, 8 November 2002

  18. New Sampling Calorimeter - Details EIC, 8 November 2002

  19. Systematic Uncertainties EIC, 8 November 2002

  20. Polarization-2000 EIC, 8 November 2002

  21. Necessities of having Fast & Precise Pe Measurement The Physics Consideration Precision Measurements (QCD): Neutral Current (NC) and Charged Current (CC) cross-sections very sensitive to Pe at high Q2 g Parton densities at large x Electroweak Physics: NC g qZ couplings: vq, aq CC g W boson (propagator) mass Physics Beyond Standard Model: Right-handed CC interaction Enhanced sensitivity for searching for Leptoquarks, Rp violating SUSY Example: NC cross-section Up to Q2=s=105 EIC, 8 November 2002

  22. A Comparison of Different Polarimeters PLe-g rateg rate(ng)(dPe)stat (dPe)syst LPOL: 33MW 0.1KHz1000 g/pulse1%/min~2% pulse lasermulti-g mode(all bunches) i.e. 0.01 g/bc1%/(>30min) (bc=bunch crossing)(single bunch) TPOL: 10W 10MHz0.01 g/bc1-2%/min~4% g cw lasersingle-g mode(all bunches)<2% (cw=continuous wave)(upgrade) New LPOL: 5kW 10MHz1 g/bc0.1%/6sper mill cw laserfew-g mode(all bunches) 1%/min (single bunch) Fabry-Perot Cavity Expected precision 0.7W EIC, 8 November 2002

  23. A High Gain Fabry-Perot Cavity Sg Use Fabry-Perot cavity to amplify laser power: (A proven technology at Jefferson Lab) HERA e beam Linearly polarized photons Circularly polarized photons All optical components are fixed rigidly on an optical table EIC, 8 November 2002

  24. Fabry-Perot Cavity Final cavity Mount for travel EIC, 8 November 2002

  25. Fabry-Perot Cavity - Details beam pipe bellows ‘laser axis’ EIC, 8 November 2002

  26. Beam intensity after cavity (Gaussian in principle) Intensity beam scan measurement x y EIC, 8 November 2002

  27. Laser Cavity Timelines EIC, 8 November 2002

  28. Photon Detection and Systematic Uncertainty of Pe New LPOL (few-photon mode):Existing LPOL (multi-photon mode): Compton and Bremsstrahlung edges Up to 1000 g produced per pulse clearly visibleSignal/background ratio improved Background determination and > 5TeV measured in the detector! Calibration easy Calibration difficult (dPe)syst: per mill level expectedNon-linearity g main syst. error Sg=-1 Sg=+1 Sg=+1 Sg=-1 EIC, 8 November 2002

  29. Summary on Laser Cavity New polarimeter with a Fabry-Perot cavity: High statistics precision: Large gain in cw laser power (~104) 0.1% every 6s (all bunches) 1% every minute (single bunch) Small systematic uncertainties: Few-photon mode Per mill level Fast and precise measurement of Pe: Valuable feedback for HERA machine to achieve maximum polarization Necessary to fully exploit the physics potential at HERA after upgrade Cavity prototype being tested at LAL, Orsay Final set-up will be installed during the shutdown in spring 2002 EIC, 8 November 2002

  30. Polarization after Lumi Upgrade EIC, 8 November 2002

  31. TPOL/LPOL Ratio EIC, 8 November 2002

  32. Conclusions EIC, 8 November 2002

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