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The Second Generation HAPPEX Experiments

Kent Paschke for The HAPPEX Collaboration California State University, Los Angeles - Syracuse University - DSM/DAPNIA/SPhN CEA Saclay - Thomas Jefferson National Accelerator Facility - INFN, Rome - INFN, Bari - Harvard - Indiana University -

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The Second Generation HAPPEX Experiments

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  1. Kent Paschke for The HAPPEX Collaboration California State University, Los Angeles - Syracuse University - DSM/DAPNIA/SPhN CEA Saclay - Thomas Jefferson National Accelerator Facility - INFN, Rome - INFN, Bari - Harvard - Indiana University - University of Virginia - University of Massachusetts - Florida International University - University of New Hampshire - Massachusetts Institute of Technology - College of William and Mary in Virginia (Thanks to Rich Holmes for .ppt from PAVI ’04) The Second Generation HAPPEX Experiments

  2. Strangeness in the Nucleon • Spin • Longitudinal momentum • Strange mass • Strange vector FF

  3. PVES Leading contribution to parity-violating scattering asymmetry is from interference of EM and weak exchange amplitudes

  4. PVES and strange form factors For hydrogen: => Measurement of APV yields linear combination of GsE, GsM Related at Q2=0 to s,s.

  5. The HAPPEX Experiments • A look back: HAPPEX, ep Q2=0.5 (GeV/c)2 • HAPPEX-H: ep, Q2=0.1 (GeV/c)2 • HAPPEX-He: e 4He, Q2=0.1 (GeV/c)2 • PREX: ePb, Q2=0.01 (GeV/c)2

  6. Hall A Proton Parity Experiment (E91-010) ep at Q2=0.5 (GeV/c)2, 12.3 degrees GsE + 0.392GsM= 0.014 ± 0.020 (exp) ± 0.010 (FF) Phys. Rev. Lett. 82:1096-1100,1999; Phys. Lett. B509:211-216,2001; Detailed paper accepted for PRC - arXiv nucl-ex/0402004 A look back: HAPPEX

  7. HAPPEX results APV = -14.92 ppm ± 0.98 (stat) ppm ± 0.56 (syst) ppm

  8. The next step • Increase sensitivity • Choose different Q2 range • Separate GsE , GsM => Two new experiments at smaller Q2

  9. HAPPEX-H (JLAB E99-115) • Polarized e- on 1H • Q2 = 0.1 (GeV/c)2, qLAB = 6 • APV = 1.6 ppm • A = 5% (stat) + 2.5% (syst) => 80 ppb (stat) + 40 ppb (syst)

  10. Helium and strange form factors For helium: => APV sensitive only to GsE

  11. HAPPEX-He (JLAB E00-114) • Polarized e- on 4He • Q2 = 0.1 (GeV/c)2, qLAB=6 • APV = 8.4 ppm • A = 2.2% (stat) + 2.1% (syst) => .18 ppm (stat) + .18 ppm (syst)

  12. Experimental impact

  13. Experimental impact

  14. Tough new measurement: How do you do it? • Small forward angle => new Septum magnets • High statistical precision => Thick new targets, high current, rad-hard integrating detectors, improved DAQ, new photocathode • High relative accuracy => improved polarimetry, new integrating focal plane profile scanner • High systematic accuracy => improved polarized source, close attention to beam optics, lumi monitor.

  15. Overview Hall A Polarized source Injector CEBAF

  16. Septum magnets • Minimum scattering angle 12.5° -> 6.0° • Installed and commissioned 2003-2004

  17. 100 x 600 mm HAPPEX-H Detector geometry Hydrogen geometry Cerenkov detectors overlap the elastic line above the focal plane : ‘L’ geometry design He detector = (H detector) / 2 ! 12 meter dispersion sweeps away inelastic events

  18. Assembly at Saclay PMT Brass-quartz stack Light guide Filter box

  19. Luminosity monitors • Target boiling • Beam parameters • Electronics noise ppm CurrentmA Tested to ~200 ppm resolution, expecting about ~100 ppm

  20. Target cells "Beer can" – 15 cm, worked well for HAPPEX-I New "race track" design – 20 cm, boiling untested

  21. Luminosity Fluctuations • Beer can cells good enough, as measured in HAPPEX • “Racetrack” cells never tried (Transverse flow good, curvature of window bad) • Cold (6.6K), dense (230 psi) cryogenic 4He gas target… “boils”! Widths go down with increasing raster… … and UP with increasing current!

  22. Polarimetry • Møller: Main uncertainty is foil polarization; p/p = 3 – 3.4% expected • Compton: Added electron recoil detector since HAPPEX-I; p/p = 2% in ~1 hour seen – 1.3% probably achievable at 3 GeV • Big challenge for PREX – high current, low energy. Plan to upgrade Compton with green laser => 1% in ~16 hours Compton GEANT4 monte carlo

  23. Compton Polarimeter • Main Challenge: extreme requirements on halo/tail are necessary to reduce background • 100 Hz / mA at 5mm from the beam centroid (10-10)! Photon detector Electron detector

  24. Profile scanners Q2 measured at low current with VDCs... ... verified and monitored at high current with scanners.

  25. Beam Requirements Property Nominal Jitter (30 Hz) Hel corr (run) Energy 3.2 GeV < 80 ppm < 13 ppb Current 100 A < 1000 ppm < 600 ppb Position 0 < 12 m < 2 nm Angle 0 < 12 rad < 2 nrad Halo <100 Hz/A @ 5 mm Specifications driven by sensitivities and estimates of quality of corrections. CASA and EGG have worked closely with HAPPEX to meet these requirements

  26. Polarized source • Pockels cell voltage (PITA) used to tune AQ, Dx • Intensity Attenuator (IA) • PZT mirror • IHWP for slow helicity reversal • RHWP for control of position/intensity asymmetries • Superlattice photocathode: >80% polarization, 100 A

  27. Controlling Position Differences Identify and control sources of position differences • Intrinsic birefringence gradient in the Pockels cell • Steering from distortions due to piezo-electric deformation of the Pockels cell • Analyzing power gradients Lisa Kaufman, Brian Humensky, Gordon Cates, Ryan Snyder, Kent Paschke, and the EGG.

  28. ITS Laser Room Studies in the laser room conducted over the past year have been crucial in developing our understanding of the sources of position differences. • Characterization of Pockels cells on parameters relevant to sources of position differences • Identification and characterization of the history effect in optical properties of the Pockels cells • Development of alignment techniques to reduce effects from Pockels cell steering

  29. Injector Beam Studies • Electron beam studies allows studies of effects from the photocathode, as well as other idiosyncratic elements such as vacuum windows. • Set points for source elements (PC voltages, rotating waveplate angle) can only be determined from beam data. • Injector transmission becomes an important issue in getting the well-tuned beam to the Hall.

  30. Phase Trombone • Goal: vary betatron phase while preserving the shape and orientation of • the phase space ellipse • implemented with eight existing quads at the beginning of the • Hall A arc • Allows for independent betatron phase control in horizontal and • vertical planes • Uses: • Allows one to trade off position and angle differences • Periodic phase changes can be used to randomize or reverse the • sign of position differences

  31. HAPPEX Has Started • Installation started June 4, optics commissioning done June 9 • Luminosity limited by septum heating, improvement possible • Progress on beam conditions (Helicity-correlated, Compton halo), spectrometers, detectors, target

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