1 / 51

The G0 Experiment

The G0 Experiment. Fatiha Benmokhtar Carnegie Mellon University Jlab Users Group Meeting, June 17 th 2008 fatiha@ernest.phys.cmu.edu. Outline. Strange quark contribution to the nucleon properties (special interest on the electromagnetic properties).

yaholo
Download Presentation

The G0 Experiment

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The G0 Experiment Fatiha Benmokhtar Carnegie Mellon University Jlab Users Group Meeting, June 17th 2008 fatiha@ernest.phys.cmu.edu

  2. Outline • Strange quark contribution to the nucleon properties (special interest on the electromagnetic properties). • G0 experiment: Forward and Backward angle. • Status of the G0Backward angle experiment analysis. • Expected results (Soon!!!  )

  3. Nucleon constituents valence « sea= virtual pairs » • - The sea contains all flavors, but • the u and d sea can’t be distinguished from the valence • the heavier quarks (c,b,t) are too heavy to contribute much • Strange quark is the natural candidate to study the sea. With how much do virtual strange pairs contribute to the structure of the nucleon ?

  4. Strange Quark Contribution to the Nucleon Properties • Mass: Hyp -> p-N ->  0 to 30 % with big theoretical uncertainties. • Longitudinal Momentum: DI nm-Nucleon scattering (NuTeV) . For x <0.1 • Spin: • .n-p elastic scattering (E734 BNL) • Polarized Semi-Inclusive DIS (HERMES) • PQCD predicts -0.1

  5. Strangeness Contribution to the Nucleon Electromagnetic Properties Goal:Determine the contributions of the strange quark sea ( ) to the charge and current distributions in the nucleon : “strange form factors” GsE and GsM How do we measure them?

  6. g Z Strange Form Factors sin2qW = 0.2312 ± 0.00015 Charge symmetry -> ? measured

  7. Parity Violation Asymmetry • Scatter polarized electrons off unpolarized target, • Asymmetries of the order of ppm Electric Magnetic Axial • Proton target • Helium target • Deuteron target • (static case) -Complete calculation by Schiavilla et al., is available. - Enhanced sensitivity to Axial form factor.

  8. Superconducting Particle Coils Detectors Beam LH Target 2 G0 (JLab) 2003-2007 SAMPLE (MIT-Bates) 1998-2002 HAPPEX I (Jlab) 1998-2002 HAPPEX II (JLab) 2004-2005 PVA4 (MAMI) 2002-2008 0.1, 0.23 (0.48) 0.12 - 1.0 (0.23, 062) 0.04, 0.1 0.48 0.1 Q2 (GeV/c)2 B F F F/B F/B Angle H,D H H, 4He H H, D Target GEs + 0.4 GMs GEs , GMs GEs,GMs Ges,GMs ,GA(p+n) GMs, GA(p+n) Separation PV. Experiments Forward Backward • HAPPEX-III 2009 at 0.6 GeV2

  9. G0 Programin Hall C of Jefferson Lab • Forward angle e +p …04 • Backward anglee+ p ...06-07 • Backward anglee+ d …06-07

  10. G0 Forward Angle(2004) Collimators e- Target Elastic cut Pions Inelastic protons Focal Plane Detectors (FPD) High Q2 • One measurement on LH2 • Ee = 3.045 GeV, 31 MHz beam str. • Recoil proton detection (52o < p <76o)  0.12 ≤ Q2 ≤ 1.0 GeV2 • Counting experiment • Time-of-flight electronics Low Q2

  11. Results from the Forward angle G0 Backward Compared to ANVS (“No VectorStrange”) EM form factors : Kelly PRC 70 (2004) 068202 D.S. Armstrong, et al., PRL 95, 092001 (2005) Examining full data set, probability that GEs+hGMs ≠ 0 is 89%

  12. Global Analysis at Q2 ~0.1GeV2 • Contains the term • R. Young et al., Phys. Rev. Lett. 99, 122003 (2007) • Global fit of all the existing forward angle data • -If SAMPLE result is used for the axial form factor GAe • GEs = 0.002 +- 0.018 & GMs = -0.01 +- 0.25 • - If GAeis taken fromZhu et al.,PRD 62 (2000) 033008 • GEs= -0.011 +- 0.016 & GMs= 0.22 +- 0.2 More measurements of the axial form factor are needed. G0Backward angle! 

  13. G0 Backward Angle Experiment(06-07)

  14. The G0 Backward Collaboration G0 Spokesperson:Doug Beck (UIUC) California Institute of Technology, Carnegie-Mellon University, College of William and Mary, Grinnell College, IPN Orsay, JLab, LPSC Grenoble, Louisiana Tech. Univ., New Mexico State University, Ohio University, TRIUMF, University of Illinois, University of Kentucky, University of Manitoba, University of Maryland, University of Winnipeg, Virginia Tech, Yerevan Physics Institute, University of Zagreb Analysis Coordinator: Fatiha Benmokhtar (CMU) Students: Carissa Capuano(W&M),Alexandre Coppens(Manitoba),Colleen Ellis(Maryland) ,Juliette Mammei(VaTech),Mathew Muether(UIUC),John Schaub(NMSU),Maud Versteegen(LPSC), Stephanie Bailey(Ph.D. W&M, Jan ’07)

  15. G0 Backward Angle • Electron Beam: 362 and 687 MeV -> Q2: 0.23 and 0.62 GeV2 • Turn-around of the magnet, change polarity • Electron off LH2 or LD2 target, electron detection :Θ = 108°. • Add Cryostat Exit Detectors (9 CEDs per Octant)-> separate elastic and inelastic electrons in the CED*FPD space. • Aerogel Cerenkov detector per octant for/e separation. (p < 380 MeV/c) Cerenkov FPD CED e Beam

  16. Sup. Cond. Magnet (SMS) Detectors (Ferris Wheel) FPD Target service module G0 beam monitoring Detectors(Mini-Ferris wheel) CED+Cherenkov Spokesman

  17. Beam Parameter Achieved (IN-OUT)/2 “Specs” Charge asymmetry 0.09 +/- 0.08 2 ppm x position difference -19 +/- 3 40 nm y position difference -17 +/- 2 40 nm x angle difference -0.8 +/- 0.2 4 nrad y angle difference 0.0 +/- 0.1 4 nrad Energy difference 2.5 +/- 0.5 34 eV Beam halo < 0.3 x 10-6 10-6 Beam Specifications • 2ns beam structure • 86 % longitudinal polarization • Helicity changed every 1/30 sec (MPS). • Form Asym. from a pseudo-random quartet structure in helicity (+--+ or -++-). • 2 half wave plate states IN/OUT • Helicity correlated beam properties -> false asymmetry.Correction : linear regression: Very smallin our case (ppb)

  18. Scalers Scalers Altera FBGA256 Scalers Altera FBGA100 Scalers Altera FBGA256 Scalers Simplified Electronics Scheme (for one Octant) Coincidence with the BPO CEDi*FPDj coincidences electrons 9 CED CED electrons YES 14 FPD FPD CED pions pions Cerenkov NO .Read Scalers for each CED*FPD combination -> Build the coincidence matrix. FPD • Electron trigger: CED*FPD*Cerenkov • G0 backward uses 2 kinds of Trigger: • Pion trigger: CED*FPD no Cerenkov

  19. Electron Yield (Hz/μA/Oct) 90C 120 C LH2, 362 MeV LH2, 687 MeV 70 C 45 C 45 C LD2, 362 MeV LD2, 687 MeV

  20. Previous experiments GEs+ GMs Background corrections: Corrections from inelastic electrons Background from target walls Pion asymmetry contamination Unblinding G0Back Analysis Strategy LH2, LD2 Raw Asymmetries, Ameas 687 & 362 MeV Blinding Factor (Mult.) Instrumental & Beam corrections: Rate corrections from electronics Helicity-correlated beam properties Beam Polarization correction   4 separate blinding factors      EM radiative corrections LD2 Aphys LH2 Aphys GEs GMs GAe  Q2 Determination

  21. G0 Analysis Four Passes per Analysis Replay Analyzer Database . Pass 1: Uncorrected yields & blinded asymmetries . Pass 2: Scaler counting correction ( the famous ‘problem’!  ) . Pass 3: Electronic correction (deadtime, randoms, contamination) . Pass 4: Linear regression correction

  22. NA Scaler Counting ‘Problem’ • An occasional bit drop in a North American scaler was traced down to trigger electronics. Was noticed at high rates: LD2 target at 362 MeV. This was fixed during the run (Jan07) • Pulser data • -Simulation Exaggerated re-production with a Pulser • Problem blind to helicity. Uncut 7 6 5 4 3 • Test by cutting data; compare with • French octants. • Confirmed by unchanged asymmetry after fix 5 cut removes ~1% of our data for 362MeV LD2,which is the worst case!  Effect on Asymmetry Cut on yield

  23. Rate Correction for Electronic Related Effects • Dead Time and Randoms in CEDxFPD coincidences and cerenkov electronics. • All the electronics chain was simulated. • Current scan runs ElectronMeasured-Corrected Yield ElectronMeasured-Corrected Yield No Dead Time Measured Corrected LD2-362 MeV (Hz/A) LD2-362 MeV (Hz/A) No Dead Time Corrected Measured A A Global correction: ~ 2-4% to the asymmetry in the elastic locus.

  24. Four Pass Asymmetries(LH2 687 MeV) 1-Raw asymmetries 2-Scaler counting correction Asymmetry (ppm) Asymmetry (ppm) 3-Electronic corrections Asymmetry (ppm) 4-Linear regression correction Asymmetry (ppm)

  25. LH2 687 Field Scan Gaus + linear + “elastic” fit to data \ Gaus + linear + “elastic” fit to data Gaus extracted from fit (background) Gaus extracted from fit (background) • Nominal field current set at 3500 A. • Vary the field and study the CED*FPD yield. Data Data Total simulation Total simulation Elastic simulation with radiation Elastic simulation with radiation Inelastic + pi0 simulation (no radiation) Inelastic + pi0 simulation (no radiation) We do understand the backgrounds and work is in progress.

  26. Other Corrections • Helicity-Correlated Beam Properties: Linear Regression: • Sensitivities to helicity-correlated beam motion smaller at backward angles. Elastic Electron False Asymmetries: < 4ppb • Electromagnetic Radiative Corrections • Simulation program for radiative corrections is under development: • R~ 4%(preliminary.) • Transverse Beam Asymmetry: Very small: under study. • Many other small checks were done.

  27. From Asymmetries to Strange Form Factors • Proton See: J. Liu PhD. thesis, UMD 2006. • Deuteron Ref:Diaconescu, Schiavilla & van Kolck, PRC 63 (2001) 044007 (Addition of the 2body currents corrections)

  28. From Asymmetries to Strange Form Factors Isoscalar sff (Estimated) to be extracted • We will use the best and up to date inputs for the quantities going into the ai coefficients. • Solve the system for the G0 Forward ( proton target) and G0 Backward kinematics (proton and deuteron targets)

  29. - Error bars dominated by statistics. - Systematic experimental: backgrounds  Small- Systematic from the nucleon form factors Expected G0 Results

  30. G0 Summary • G0 Forward angle • GEs+nGMsfrom Q2=0.12 to 1 GeV2 • Strange quark contribution non-zero at 89% confidence level • Nicely consistent with emerging picture at Q2=0.1 GeV2 • Gave some clues about where to look next (HAPPEX-III) • G0 Backward angle • Provide clean separation of GEs, GMs, and GA at Q2=0.23 and 0.6 GeV2 • Data Analysis almost at the end, complete separation coming soon! 

  31. Additional Program to theG0 Experiment • Parity-violation in electro and photo excitation of the Delta resonance: - inelastic electron • - photopion asymmetries). • - Analysis in good progress • Beam normal asymmetries and two-photon exchange. - - • - Analysis in good progress.

  32. Backup Slides

  33. a1 xsection a0 a2 a3 a4 Ebeam = 680 MeV, qe = 100° (Deuteron)

  34. At 685 MeV: vs scattering angle via interpolation

  35. Transverse Polarization Data (G0 backward) • contains intermediate • hadronic state information magnitude of transverse asymmetry depends on direction of transverse beam polarization Blinded

  36. Elastic Region: G0 Inelastic Region: N D G0: N →  • Measurement:Parity-violating asymmetry of electrons scattered inelastically • ANΔ gives direct access to GANΔ • Directly measure the axial (intrinsic spin) response during N →Δ+ transition • Will find GANΔ over a range of Q2 • 0.05 GeV/c2 < Q2 < 0.5 GeV/c2. • First measurement in neutral current process • Data: Inelastic electrons measured by G0 • Scattered from both LH2 and LD2, each at two energies (362MeV & 687MeV) Asymmetry (ppm) vs Octant (LH2 @ 687MeV) IN • BLINDED Asymmetry (ppm) OUT Raw Asymmetry (averaged over inelastic region)

  37. Measurement of the Parity Violating Asymmetry in the N →Δ Transition Q2 Range of G0 Measurement expected precision (1) = 2(1sin2W) = 1 (Standard Model) (2) = non-resonant contrib. (small) (3) = 2(14sin2W) F(Q2,s)  (N-D resonance) At tree-level: Asymmetry (ppm) vs Octant (LH2 @ 687MeV) • F contains kinematic information & all weak transition form factors • Extract GANDfrom F BLINDED Raw Blinded Asymmetry (averaged over inelastic region)

  38. Pion Asymmetries LH2 687 MeV Longitudinal – corrected for transverse : BLINDED Blue data points : Half Wave plate “in” Red data points : Half Wave plate “out”

  39. BLAST Results • C. Crawford et al., Phys. Rev. Lett. 98, 052301 (2007)‏

  40. Nucleon Electromagnetic Form Factors . Measured with precision over wide range of Q2 . (10~15% for neutron electric F.F. at low Q2) -A lot of improvement over the last decade with double polarization exp. . Preliminary results from blast didn’t improve Gen much. Accessible via parity violating amplitudes, but how?

  41. Different Nucleon EM FF Parametrizations

  42. Some examples of corrections Deadtimes (%) • Deadtime corrections to the yield • Simulated the complete electronics chain: LH2, 687 MeV LH2, 687 MeV, 60 mA ~ 7% LH2, 362 MeV, 60 mA ~ 6% LD2, 687 MeV, 20 mA ~ 9% LD2, 362 MeV, 35 mA ~13% (work in progress ) LH2, 362 MeV • Randoms corrections • LH2 randoms small • LD2 randoms significant, esp. inelastic el. • measure directly!

  43. Cerenkov Efficiencies • Electron detection efficiency • Determined using three different techniques • Does not change asymmetry Four CerenkovDetectors CED/FPD Coincidence electron pion

  44. Quartz PMTs • Aerogel Cerenkov counters for p/e separation (LD2) • 4 - 5 in. PMTs each • boroscilicate glass very sensitive to neutrons • replace with quartz • beam current for LD2 limited by • high real p rates  • (neutron) Ch. accidentals • quartz tubes allow increase in effective electron efficiency by ~x2 • current limits 20 mA (35 mA) at 687 (362) MeV • final tubes installed over Xmas break boroscilicate quartz Note difference in vertical scales

  45. Four Pass Asymmetries (LD2 362 MeV) Four Pass Asymmetries (LD2 362 MeV)

  46. Data Quality (LD2 362MeV) Most of the Data is good quality BUTNA Scaler Data at high rates Counts (log scale) Counts (log scale) Yield Yield Yield (Hz/uA) Yield (Hz/uA) Counts (log scale) Asym. Counts (log scale) Asym. CED# Asymmetry (ppm) Asymmetry (ppm) FPD#

  47. Global Analysis at Q2 ~0.1(GeV/c)2 68% CL 95% CL Leinweber et al. • 1- R. Young et al., Phys. Rev. Lett. 97, 102002 (2006) • 2- R. Young et al., Phys. Rev. Lett. 99, 122003 (2007) • - Added the latest Happex point. • Ges = 0.002 +- 0.018 & Gms = -0.01 +- 0.25 • If Zhu et al. is used: • Ges = -0.011 +- 0.016 & Gm^s = 0.22 +- 0.2 • J. Liu et al, Phys. Rev. C 76, 025202 (2007) • - Using Zhu’s model value for GeA. • Ges = -0.006 +- 0.016 GMs =0.33 +- 0.21 There are two other fits one from K. Paschke And one from F. Maas..

  48. Λ Strange Form Factors Calculations at Q2=0 and If msis negative, then s and sbar would make (+) overall contribution tomp. Hannelius, Riska + Glozman, Nucl. Phys. A 665 (2000) 353 convention: positive charge radius  negative radiusrs  GEs < 0  s-quark on the outside see R. Jaffe, PLB 229 (1989) 275 or Geiger & Isgur, PRD 55 (1997) 299

  49. Electromagnetic Radiative Corrections Follow process of Tsai [SLAC=PUB-848] 1971. Compute asymmetry [ ] based on the kinematics at the reaction vertex after the radiative emission. This is compared to Born asymmetry calculation [ ] with Both and are calculated including ionization losses in the target prior to scattering. Target Energy A0rc A0 tree Rccorrection LD2 687 -46.6 -48.43 3.7% LD2 362 -13.64 -14.17 3.9% LH2 687 -36.81 -38.22 3.8% LH2 362 -10.1 -10.49 3.9% Preliminary Raw Blinded LH2 687 With Radiative Effects LH2 687 Without Radiative Effects • Geant Strategy: • Generate electron at random point in target • Assign random scattering direction and energy to the electron • Calculate cross section and asymmetry for that scattering process

  50. Nucleon constituents valence « sea= virtual pairs » • - The sea contains all flavors, but • the u and d sea can’t be distinguished from the valence • the heavier quarks (c,b,t) are too heavy to contribute much • Strange quark is the natural candidate to study the sea. With how much do virtual pairs contribute to the structure of the nucleon ?

More Related