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The G 0 Experiment Strange quark contribution to proton structure

The G 0 Experiment Strange quark contribution to proton structure. Kazutaka Nakahara KEK for the G 0 Collaboration:

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The G 0 Experiment Strange quark contribution to proton structure

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  1. The G0 ExperimentStrange quark contribution to proton structure Kazutaka Nakahara KEK for the G0 Collaboration: Caltech, Carnegie-Mellon, William&Mary, Grinnell College, Hampton, IPN-Orsay, LPSN-Grenoble, JLab, Kentucky, LaTech, NMSU, TRIUMF, UIUC, U Manitoba, U Maryland, UNBC, U Winnipeg, VPI, Yerevan SPIN2006 Kyoto 10/6/2006

  2. Flavor Decomposition of Nucleon Form Factors Neutral Weak form factor: s quark contribution Measure GZ,p !!! Determine s quark contribution to the charge and magnetization distribution of the proton Proton and neutron EM form factors (assuming charge symmetry): Spin2006 Kyoto 10/6/06

  3. Parity Violating Electron-Proton Scattering Measure at forward angles (elastic e-p) Measure at backward angles (elastic e-p and quasi-elastic e-d) Parity Conserving Parity Violating Spin2006 Kyoto 10/6/06

  4. Jefferson Laboratory linacs Injector/Source A C B

  5. Backward Angle Apparatus • Backward angle mode: • Q2 = 0.23 and 0.62 • 80A longitudinally polarized beam. 499MHz repetition rate  no TOF • Helicity flip at 30 Hz (macro-pulse, MPS), arranged into quartet pattern. • High power LH2 & LD target. 8 octant superconducting toroidal magnet. • 8 octant, array of 16 scintillator pairs per octant. Additional detectors (Cerenkov, CED) for background (pion) rejection. • FPD-CED matrix electronic/detector package  separate elastics from background. Scintillator Detector Target Superconducting Coils elastic protons detectors lead collimators beam target • Forward angle mode: • Q2 = 0.12 ~ 1.0 • 40A longitudinally polarized beam. 32MHz repetition rate for TOF. • Helicity flip at 30 Hz (macro-pulse, MPS), arranged into quartet pattern. • High power LH2 target. Capable of maintaining stable temperature/density with high power deposit. • 8 octant superconducting toroidal magnet, array of 16 scintillator pairs per octant. • Different scintillator  Different Q2. Distinguish elastic protons from background through TOF separation. • Fast electronics counting individual particle. Forward Angle Apparatus Spin2006 Kyoto 10/6/06

  6. G0 in Hall C : The key elements Superconducting Magnet (SMS) Target service module G0 beam monitoring Detectors (Ferris wheel) FPD Detectors (Mini-Ferris wheel) CED+Cherenkov Spokesman

  7. Forward Angle Data Successful run in spring 2004 • Different components separated by t.o.f. • Beam systematics understood: • 73.7 % polarization • small helicity-correlation • effect of leakage beam understood • Background under elastic peak is main analysis issue Corresponds to: 701 h at 40 A (100 C) 19 x 106 quartets 76 x 106 MPS Spin2006 Kyoto 10/6/06

  8. Strange Quark Contribution to Proton

  9. GE GM s s s GE s GM , Data @ Q2 = 0.1 GeV2 = -0.013  0.028 = +0.62  0.31 • Contours • 1s, 2s • 68.3, 95.5% CL • Theories • Leinweber, et al. PRL 94 (05) 212001 • Lyubovitskij, et al.PRC 66 (02) 055204 • Lewis, et al.PRD 67 (03) 013003 • Silva, et al.PRD 65 (01) 014016 http://www.npl.uiuc.edu/exp/G0/Forward

  10. HAPPEx calculation: Q2 = 0.1 GeV2 . , Data @ Q2 = 0.1 GeV2 GE GM s s GM = 0.28 ± 0.20 s GE = -0.006± 0.016 s HAPPEx He

  11. Q2 = 0.23 and 0.62 GeV2/c2 G0 Backward Angle Status • March 15 – May 1: 0.62 GeV2/c2 • - 200 hours LH2, 50 hours LD2 (at 10 A) • - 80 hours “parity quality” data w/ LH2 at 60 A • May15-18: 0.23 GeV2/c2 • - first look at LD2 at low beam current • - outstanding beam delivery • July 19- Sept 1 (0.23) / Sept 22- Dec 22 (0.62) production First hand look at data so far: - Elastic asymmetry near expected - good elastic/inelastic electron separation - pion asymmetry smaller than elastic - Deuterium data shows high background rates in Cerenkov (probably neutrons)

  12. Summary • Forward angle production run successfully completed • Results published • Phys. Rev. Lett. 95, 092001 (2005) • Interesting Q2-dependence for the strange quark contribution to the nucleon form factors • Agreement at low Q2 with previous experiments • Backward angle measurement has begun! Spin2006 Kyoto 10/6/06

  13. Backup

  14. Summary of Systematic Effects

  15. superconducting magnet (SMS) G0 in Hall C cryogenic supply beam monitoring girder scintillation detectors cryogenic target ‘service module’ electron beamline

  16. Strange Quark Contribution to Proton http://www.npl.uiuc.edu/exp/G0/Forward D. Armstrong, et al. PRL 95 (2005) 092001

  17. Blinding Factor Raw Asymmetries, Ameas “Beam” corrections: Leakage beam asymmetry Helicity-correlated beam properties Deadtime Beam polarization Background correction Aphys Unblinding GE GM + h s s Q2 Elastic form factors Analysis Overview

  18. Helicity-Correlated Beam Parameters • How much does the yield change when the beam “moves”?  understood (simulation & data agree) • ‘Instrumental’ (false) asymmetries • e.g. if beam current changes in helicity-correlated manner • e.g. if beam position on target changes in helicity-correlated manner False asymmetries from helicity-correlated parameters small (~10-8) compared to physics asymmetry (~10-5 – 10-6)

  19. Strange Quark Contribution • Strange quark contribution to asymmetry depends on: - ANVS = No vector strange asymmetry - EM form factors (Kelly parametrization) http://www.npl.uiuc.edu/exp/G0/Forward

  20. Strange Quark Contribution to Proton

  21. Where Were We? • From HAPPEX H preprint nucl-ex/0506011 Similar angular kinematics to G0

  22. New features and specificities Polarized source and beam • High polarization has been reached routinely using superlattice GaAs cathodes • New Fiber laser for Hall C (adjustable pulse repetition rate) • Allows flexible time structure (1-2h for setting) : 32 ns used for Cherenkov study • 780 nm is at polarization peak (P ~ 85%) for superlattice GaAs • 60 mA of low energy beam • New optics, beam dump and halo issue handled Moeller polarimeter in Hall C • Energy smaller than 800 MeV (design) • Need to move quadrupoles closer to target • Difficult tune (beam position, magnet settings) • Finally successful at 686 MeV • 1 um foil = -86.36 +/- 0.36% (stat) • 4 um foil = -85.94 +/- 0.33% (stat) • Systematic error  2 %, expected to be reduced

  23. Commissioning (I) Beam properties • Hall C instrumentation OK • Beam properties • 35 h IN and 42 h OUT at 60 mA (LH2) • Adiabatic damping, PITA, RWHP, IA • Room for improvement (position feedback) • Halo within a 6 mm diameter was determined to be < 0.3 x 10-6 (spec : 10-6 ) Targetand Lumi detectors • LH2 and LD2 target (“Flyswatter” and gas target for cell contribution) • Target boiling from Lumi detectors • Intensity up to 60 mA (limitation by window on beam dump) • Very flat behavior (rates/beam current) • RatioLD2:LH2:C12 are the ones expected

  24. Particle ID : CED-FPD + Cherenkov 60 mA, LH2 10 mA, LD2 (rates in Hz/mA per octant) Electrons Pions

  25. Loss/random issue Fraction (%) of lossI Fraction (%) of randomI2 LH2 60 mA LD2 10 mA

  26. IN OUT Asymmetries : Electron plane and LH2

  27. IN OUT Asymmetries : Electron plane and LH2

  28. Data taking in 2006 (I) First period of running at 682 MeV • Commissioning and data taking … in a row !! • As usual a risky business and a scary/tough period !! • Many new features handled successfully • Beam : low energy … but no compromise on intensity and Parity Quality • New settings (polarimeter, target, …) • New set-up (CED, Cherenkov, electronics …) • Analysis underway (remember this ended … 15 days ago !!) Remained to be fixed for running in the Fall • Work/tests underway to reach 60 mA with LD2 • Cherenkov (anode current and random coincidences) • Gas flow in diffusion box (Ar (not working), CO2), gain/HV reduction, M > 2 • CED-FPD (random/loss) • Use backplane scintillators of FPD counters (factor 10 reduction)

  29. G0 Backward angle … What’s next in 2006 Still a long way to go … and maybe some new challenges at 362 MeV • Adiabatic damping • Halo issue (if due to processes in residual gas) • Test run underway this week at JLab • More work on Moeller polarimeter Hopefully by the end of 2006 … +

  30. Lab Update Slides – Sept. 15

  31. G0 362 MeV Update D. Beck UIUC Sept. 06 • Hydrogen data taking at 362 MeV completed • 86 C out of ~ 120 C possible as scheduled • 170 C proposed: 80 mA for 30 d • 75% polarization proposed, 84% delivered • Very clean hydrogen elastic signal • all backgrounds total ~ 5-10% (quasi) elastic electrons Hydrogen data (Aug.) Deuterium test run (May) CED Rate (kHz/mA) FPD

  32. G0 362 MeV: Deuterium Tests • High singles rates in Cherenkov detectors with deuterium target • traced to low energy neutrons capturing in boroscilicate glass PMT windows: B(n,a)Li • measurements at NIST, Grenoble confirm effect • each a produces 6 p.e. • recalibration of NIST neutron beam flux (10 p.e. → 6 p.e.) • PMTs with quartz windows • reduce counting rates for ~thermal neutrons by x100 (NIST, Grenoble) • Based on July/August testing • various combinations of 5 in. boroscilicate and 2 in. boroscilicate and quartz tubes • extrapolate from comparison of LH2 and C targets • with new 5 in. quartz tubes for Cherenkov detectors: bottom line Expect 0.5 – 1.5 x LH2 rate (→ successful run) • Successful reduction of FPD accidentals (x4) • alternate front and back tubes

  33. 362 MeV Beam • Helicity-correlated beam properties well within spec • Beam polarization • measurement with Moller not feasible • std. solenoid field not compatible with beam transport • chkd longitudinal polarization • concurrent Hall A, Mott measurements at beginning of run • periodic Mott measurements throughout run • individual measurements average ~84±1.5%

  34. G0 362 MeV Online LH2 Asymmetries • Low backgrounds (5-10%), small deadtimes (4-8%) • BLINDED online results • fraction of data set • no corrections for h.c. beam parameters, deadtime, …

  35. G0 362 MeV Online LH2 Asymmetries Elastic P R E L I M I N A R Y Background Octant Octant

  36. G0 362 MeV Online LH2 Asymmetries • Low backgrounds (5-10%), small deadtimes (4-8%) • BLINDED online results • fraction of data set • no corrections for h.c. beam parameters, deadtime, … • Also measured asymmetry with transverse polarization to correct longitudinal asymmetry • beam angle limited to ~ 50 mr from longitudinal • asymmetry in octant azimuthal scattering angles limited to ~ 20 mr • correction < 0.1 ppm

  37. G0 362 MeV LH2 Transverse Asymmetry • BLINDED online results • no corrections for h.c. beam parameters, deadtime, … Transverse: Elastic P R E L I M I N A R Y Octant

  38. Outlook for 687 MeV • Direct resumption of production data-taking as soon as halo/background from April restored • Lower accidental rates in FPDs (as in summer run) • Expect switch to LD2 near end of October (as soon as tubes arrive • possible LD2 test (~ 2 days) in early October to finalize plans for trigger with new Cherenkov tubes • Expect near 100 C of data for both LH2 and LD2 at 687 MeV assuming • Cherenkov tubes arrive before end of October • rate projections for LD2 correct

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